Dear D.,
I can SO relate to this. Your MIL sounds so clueless. Some people are just not self-aware. What you describe is just ridiculous.
My in-laws favor the youngest son, I’ll call him Tom. No, they worship him. I realized this years ago, before kids. Tom’s wife Kim also would talk with MIL about me, in front of me. So, I was not surprised when Tom/Kim’s kids came along that they “hung the moon” and my daughter would be treated like your son is being treated. My daughter was in the hospital for 6 surgeries/7 months and my MIL says “oh, poor Heather (my niece)” ‘cause she has asthma. Now, I know you can die from asthma but my daughter almost died twice due to complications from surgeries. My MIL remarked when my child was in pain “sometimes you have to deal with things you don’t want to.” This was my baby, who had a colostomy (not to mention her indwelling IV).
Now that Heather is 17 and dresses like a tramp, NOW the MIL wants to put her down (in my presence) and draw me into criticizing her. No way am I going to be baited like that. She can forget about it.
My daughter never was close to MIL because of this, always preferred my mother. It hasn’t been too traumatic, though. Never do my in-laws comment about my daughter’s good grades, behavior, etc. I just quit bringing it up.
I also read the following on an etiquette topic on topix.com and it’s kind of how I feel:
“I never call to invite her anywhere, never include her in things I do, never tell her anything, never talk to her except as if she were a total, somewhat dimwitted stranger someone felt sorry for and so invited to wherever I am that she happens to be. I am never, ever rude or sarcastic, just distant and mildly pleasant, talking only about the most banal things.”
I'm not sure if I would cut them out abruptly or completely though...
I’ve done a lot of praying and realize my MIL was messed up by her own parents (took 20+ years to figure all of it out). And she & my SIL are so much alike, but truly, I don’t miss their friendship. I just keep that side of the family at arm’s length.
Don’t know if this helps; however, you have plenty of company, I’m sure, on this subject.
p.s. your husband gets major points for talking to them. But I doubt you’ll ever change them.