Bouncing between two PhD supervisors I'm a PhD student in engineering. I work in a small group with two professors and 5 PhD students (no postdocs). 

Both the professors "follow" my thesis as supervisor. However, they don't get along with, and they are continuously trying to pull me to their side and change my research subjects.

It's not that my project is not going well (I have 12 publications: 4 journal papers and 8 conference papers). However my two professors don't want to collaborate together and every time assign me random extra work to do for them, on various subjects, uncorrelated one with the others, and in which I'm not even expert.

All the other PhD's in my group are in the same situation. If we raise a concern about our thesis, their answer is just "now do what I ask you, we'll think to put together a thesis at the end of your PhD". 
It even happened that I sent a full paper to one of them, ready to be submitted, just to be told "If you want to publish this, you have to do this other (uncorrelated, ndr) work before". 

The worst part is that professors and researchers from other divisions know the situation and come to our group every time they need cheap work. So, one day, one of the supervisor comes to your office and says: from now you'll collaborate with professor A of dept. B on this topic. Another day, the other supervisor has lunch with some professor, comes and tells you: I need you to work with prof. X of division Y on this other topic.

Most of the time, these extra assignments are running tons of calculations and collect results, code debugging, or even external consulting for private companies. Needless to say, this is a major slow down to my research activity because I spend more than half of my time on other topics in which I'm not competent. Most of these random activities ends up without publications. I'm only publishing from my main research project.

My only luck is that I have contact in other universities and I have postdoc offers there, and that I've always had clear ideas on my thesis. So I still managed to publish my papers. Other students are not so lucky and they are at the second or even third year of their PhD without having publications nor having a clear direction for their research project.

I'll finish in less that one year and, as I mentioned, I have offers in other places. However, I'm starting to ask myself a question: Is this normal in academy? I wonder if this is the standard, and I'll find exactly the same situation in other universities or if it was just an unlucky combination of bad bosses.

I love my research activity, but if these are the working conditions, I'm starting wondering if it is worth to go on..
This seems like a mixed blessing/curse to me. It seems to be hard and frustrating, of course, but on the other hand you have two professors who, while not agreeing on much, seem to love your work. You get a lot of finalized work (publications) out of the deal. I suspect you are building a strong academic career for yourself. 

But I suggest you look for the end of the tunnel. Get the main work done somehow and find a good position without alienating either of your "patrons." I suspect that you are in a strong position in the long run and quitting would be giving up too much. 

I suspect that you are pretty good already at putting the two off at least a bit to make some room for yourself. If you can continue that, then just start to plan your exit. You won't be juggling their needs forever, I think.