Q:

layout with fragment and framelayout replaced by another fragment and framelayout

EDIT:
So after the comments below, I revisted and realized what was hanging me up.
Imagine my client list and client details activity be started by :
public class ClientsMainActivity extends FragmentActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //StudioTabOpenHelper db;
        setContentView(R.layout.main_client_activity);
    }
}

So this works great, starts up my main_client_Activity (defined in a layout below, and i call this activity when a button on my main screen is clicked):
Intent intent = new Intent(getActivity(), ClientsMainActivity.class);
startActivity(intent);

Easy the issue is, the ClientsMainActivity does not call a OnCreateView or anything, just sets the layout to the layout that defines my Fragment, and my ListFragment.  This is fine cause I am not trying to pass anything into the ClientsMainActivity, but if I have a hypothetical activity like:
SessionMainsActivity that is called when they click on the session edit of a client, then I would not be calling the SessionsMainActivity the same way (starts activity that just sets to alayout), i would want that layout set as it defines how my fragments are split up.  But I would also want to pass in data to that and then to the subsequent fragments (like which session they clicked on to be editing/mucking with.
So I wonder if the above makes sense, I am sure its a simple thing I just cannot wrap my brain around.  I have no issues calling FragmentActivities from other fragments, they take up the whole screen but it works.  So I guess the big issue is that ClientsMainActivity is from some example I found online for doing recipes that shows you how to make multiple fragments to a screen.  The thing that gets me all that FragmentActivity does is sets the content view, to a layout that does all the work it seems, so that's why I cannot figure out how I would code it to do the same thing but let me pass in values to the fragments the layout defines etc... 
END EDIT
So I am using this nice little tutorial here:
http://developer.android.com/guide/topics/fundamentals/fragments.html
It has gotten me a long way and utilizing what they say to do for the main activity, and the fragment_layout.xml, I got a nice client list on the left (Thats a listfragment) and a details fragment on the right.
Then i added the ability to edit session information on a client (or edit client details) both of which were full screen fragments.  This worked great.
Now I decided my Session edit ui would best be served splitting the information up into two panes again.
This is not working as I thought, like I said I have a main_Activity that does this in the onCreate:
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_client_activity);
}

with the main_client_activity.xml being defined in two layouts but the one for landscape tablets is here:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="horizontal"
   android:layout_width="match_parent"
   android:layout_height="match_parent">

   <fragment class="com.viciousbytes.studiotab.subactivities.ClientListView"
        android:id="@+id/client_list" android:layout_weight="1"
        android:layout_width="0px" android:layout_height="match_parent" />

   <FrameLayout android:id="@+id/client_details" android:layout_weight="1"
        android:layout_width="0px" android:layout_height="match_parent"
        android:background="?android:attr/detailsElementBackground"/>

</LinearLayout>

This all works great!  In which case I handled everything else as a full screen activity that started its own fragment:
EditSessionActivity
EditClientActiivyt  both of which use getSupportFragmentManager().beginTransaction and I could pass information into it from the .newInstance call.  
I had my session_edit.xml layout defined with buttons, textviews etc..and that was working great.  Thats what i loaded in my SessionEdit fragment "launched" by my EditSessionActivity But now since I want to split it apart I ran into a snag.  Above I defined a client_list and a client_details id, are these placeholders on my screen?  do I reference those when I wanna replace whats there with totally different fragments?
or do i build another fragment layout called something like fragment_session_layout which defines something like:
<?xml version="1.0" encoding="utf-8"?>    
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="horizontal"
  android:layout_width="match_parent"
  android:layout_height="match_parent">

   <fragment class="com.viciousbytes.studiotab.subactivities.SessionEdit"
        android:id="@+id/session_edit" android:layout_weight="1"
        android:layout_width="0px" android:layout_height="match_parent" />

   <FrameLayout android:id="@+id/invoice_details" android:layout_weight="1"
        android:layout_width="0px" android:layout_height="match_parent"
        android:background="?android:attr/detailsElementBackground" />
</LinearLayout>

Sorry don't know what to title this on the tip of my tongue of what I am asking, basically how to get two panes of fragments twice over.  THe demo online shows how to do one (and a simple ListFragment at that).
I have done all the above and I just cannot figure out how to pass into the fragment the data I need, I was using this in my EditSessionActivity:
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    int clientID = getIntent().getIntExtra(THE_SELECTED_CLIENT, -1);            
    int sessionID = getIntent().getIntExtra(SELECTED_SESSION,-1);
    SessionEdit edits = SessionEdit.newInstance(this.getBaseContext(), false, clientID, sessionID);
    mUIListener = (OnUpdateUI)edits;
    getSupportFragmentManager().beginTransaction().add(android.R.id.content, edits).commit();
}

that worked, but to try to adhere to the earlier fragment example, i assumed my EditSessionActivity was sorta like making another MainActivity (cause it has two panels in it like the main one).  so I recoded the onCreate in EditSessionActivity with this:
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);      
    setContentView(R.layout.edit_session_fullview);
}

Which after fighting in my EditSession fragment dealing with the onCreateView, I got this to finally work but couldn't pass in the data cause there is no instantiation of the object using like the previous onCreate which had the edits=SessionEdit.newInstance(...)
So is it good practice to be doing the other fragment layout that has two pains in it and starting that up when the right action is triggered.  Or is one supposed to replace the two already created fragments?? from my main_client_activity.xml somehow?

A:

I assume editing clients and editing sessions are two distinct activities. When you switch from "editing clients" to "editing sessions" mode, both the "list" and "details" panes would change? 
I would go with two layout files, instead of trying to reuse the same layout and reload fragments in it. 
If you tried to reuse the same layout, you would have to:

Change @+id/invoice_details to something like @+id/right_pane. Otherwise it would look confusing to load something related to sessions into "invoice_details" placeholder.
replace fragment definition with another FrameLayout and load either ClientListView or SessionListView (or however it's called) fragment there at runtime. 

This would add more complexity than having another layout xml file in my opinion.
So

Take your existing code that works with client list and client details
Duplicate all involved parts, and change what needs to be changed so it's now session list and session details
Remove duplication where it's easy to do (common functions go to utility classes, common layout elements to layout includes). Leave the things that are hard to de-duplicate as-is. 
Re-evaluate later, when you have more fragments, more layouts and more experience.

UPDATE, about two different approaches fragments can be embedded in activity
As the Android documentation states, there are two main ways you can get a fragment to show up in your activity:

declare the fragment in layout's XML file (<fragment class=.... />)
put a placeholder FrameLayout in layout's XML file and load fragment at runtime

First approach is fine when fragment doesn't need to receive any arguments. Like, for example, if the logic to retrieve single and only list of clients is hardcoded in fragment's code.
Second approach lets you pass arguments to the fragment, and therefore is appropriate for "details drilldown" type of fragments. 
From updated question I understand that, 

each client has a separate list of sessions
the components in play are: EditSessionActivity that hosts two fragments, one for displaying list of sessions, another for displaying session details

If that's correct, then indeed you'd need to load both fragments programmatically because both needs parameters to be passed to. So your layout would have two FrameLayouts. The EditSessionActivity would start with getting some parameters from intent ("which list of sessions are we working with?"), and load "list of sessions" fragment with these parameters. When user selects list item in that fragment, the other fragment would be loaded with session details.

