I'm with woofgang on this - it's your husband's call.
If he is comfortable with a little honesty, then maybe you should have a sit-down with your MIL and have an exchange of views.
This needn't be hostile - but maybe you can get to the root of the issues between you.
I do believe that mothers of sons have more of an issue with the woman their son chooses, than do mothers or fathers of daughters. If she has jealousy issues, then she needs to address them. the way of it is, her son is now your husband first and foremost, then your daugher's dad, and then her son, and that's the correct order of things.
Hopefully a chat with your husband will give you some direction, but i think it is his needs first over and above your MIL's.
Good luck!