Tired of My Mother-in-law living with us ... what should I do?

Talk to your wife about it. I don't think this situation is healthy. If she has 5 sister I think it would be a good idea to take a break, even just for a short while, and see how you all feel about this situation. I don't think I personally could take 13 years with my mother in law. I admire your stamina, but if it's taking its toll on your marriage I don't think it should go on.

Do you two have any kids? I encountered the same problem before , what happened was we left her with the kids all the time , she got tiered and moved out. Kids will do the job! If no kids are involved here , then your wife must reach an agreement with the whole family and  talk to them about it not  with the mother in law  so she won't feel unwanted. If it comes from one of the other  sisters telling her that they all chipped in to rent her an apartment then she might agree.

It's a delicate situation but I really think the other brothers or sisters should do more to help you out with the load. There's no reason why it should all fall on your shoulders. Your relationship with your wife shouldn't be damaged because of your mother-in-law.