Your MIL reminds me of my mother. She delegates, but micromanages; she is opinionated and voices her constant commentary, and feels shielded by the fact that what is saying is true, without giving thought to the fact that it can be hurtful; she often makes comparisons; and she is manipulative. At the end of the day however, she is my mother, and she is the only one I have; so I've learned to deal with her. Slowly, but surely, my husband has as well.
My MIL is no cake walk either, she is full of negativity, and is a back seat driver. Her way of laughing things off is to say "its a disaster" and "I'm going to panic" for the smallest mistake and infraction. Gets my blood pressure going, even though she does it in jest. She gets on my husband's last nerve and mine. Again, though, it is her way. She is my husband's only mother, and he has learned to live with her, and I will as well.
Your hubs is right, she is just being who she is. Only she can decide to make a decision to change her own behavior towards you.
You have choices. You can confront her, and hope for change, and be prepared to deal with the lack thereof; or you can change your attitude. Let it roll off your back.
For some concrete suggestions-
1. If you are called on to help for dinner, prep dishes at your own house. Two cooks in the kitchen. . . .
2. If she brags on your SIL, concur that she is lovely, and is indeed a good mother etc. Don't be contrarian if you have no reason to put SIL down.
3. If she says something untowards about your kids, be sure to quickly and quietly discount it out loud in front of your children, both of them. i.e. Baby is tearing up a magazine. MIL says what a horrible child. You say, baby is not a horrible child, or its hard work being a baby, let's put that magazine away.
4. As for your weight, and appearances, steel yourself with the thought that you are still the apple of your husband's eye. If it really gets under your skin, say so.
5. It might surprise you, but she might be bragging on you to your SIL.
Your own words really resonated with me. "I just want to feel like a part of the family without being criticized." Seems like the family dynamic includes being criticized. Looks like they are no longer on their "best behavior" and are treating you like family (for better or worse).
Good luck to you and yours, and best wishes for a happy thanksgiving.
F. B.