My sister in law irritates me to no end.  I wish my husband would talk to her, but in their family the rule of law is "don't make waves".  It's ridiculous.
I'm sorry to hear that, hopefully she naturally mellows out.
No, I don't think so.  She's 45 and cannot raise her kids.  She lives with my mother in law, and my MIL houses them, feeds them, clothes them, basically raises them, while my sister in law takes no responsibility.
Wow, that doesn't sound good. Situations like this are hard because you probably don't want to offend your family and stuff.