I used to experience and suffer like you.
I say used to because in deciding to save my marriage, which was at risk because me and hubby was always fighting over my mother in law, i decided to just totally ignore her. And by that i mean that i dont't greet her, if i cook ,its for hubby and me etc. So she is just this stranger who lives with me.
It got so bad beacause initially, hubby will just tell me to tolerate her but after all the things build up, i just blew one day and shouted back at her.
It was to the point that if anything went wrong in the house, mother in law will say its me who caused it! I have a share in the house! she doesn't! will you tolerate that? And she will not do any housework but will mess up whatever i did..the only time she does something is when dear hubby is in the house and she will do in full view of him! Very hypocritical!
It has been at least 2 years since we spoke and although i do feel bad sometimes, mostly towards hubby, i just think of the things i went thru and i think she deserves it.
I think in your case, you have to put your foot down and tell them how you feel. If not, since your hubby understands, ask him to talk to his parents. The consolation is you are not staying with them. I feel that you need to do something about it or you will prob go mad! I almost did!
If you need someone to grumble to, i drop my baby off at Bedok and pick her up every evening.