Yeah, I don't know that I'd reach out to the MIL right now. Better to do it in a neutral position when they aren't in a big tiff. You probably aren't the right person to support her right now and I can't see that it would be helpful for either your R with her in the long term or your R with him.
Also, you are not crazy. (They sound a little dysfunctional though.)
Me (46) H (42) M:14 T:18, D9 & D11 4/19 - 12/19: series of escalating BDs 9/20 - present: R and piecing