Oh wow I would be furious if I were you!!! Your MIL is definitely stepping over the line and needs to be pulled back in! Not sure how to go about it, if it was me I would probably bottle it up until I exploded, so I wouldn't recommend that! How much longer will you be living with them? I think you're doing an amazing job and are much more patient and tolerant than I would be. Can you organise a family meeting about it? Sit down all together and maybe get your husband to be the one to broach the subject - but if you do it all together, you and FIL are witnesses so your MIL can't pretend she wasn't aware of your feelings IYKWIM?

Hugs hun, here's hoping your house gets built soon!!