looking through these comments, I see I am on my own in feeling this way. While I do think it’s wicked uncool of your stepmom and dad to weaponize your non biological siblings, I just don’t understand why your mother’s family would outcast the non-bio siblings so much. I see your dad’s family as a unit, even with the divide of biological and non-biological. I feel that your mom’s family should at least be accepting of them at family events. Maybe sending the non-biological family on trips with that family isn’t good, but it really seems to me they are excluded when your whole family (dad, stepmom, you & your brother, and non-biological siblings) isn’t viewed as a family unit.

If I had kids with a deceased spouse and a new spouse, I’d want all of my children to feel loved by all parts of my family, even former ILs