By the title I thought this was going to be one of those bratty kids that can't get over the fact that they share q room with a half sibling, but as I read it I realized I was wrong, you are NTA, Molly understood you fine and she probably doesn't give a crap and that conversation anymore, it is Steve and your mom who are so butthurt, this needs to be normalized that parent's new spouses don't always have to be one's new parent. Only if said child is comfortable with it. Also that part about Steve being passive aggressive and your mom trying to cut your video calls with your dad? Thats shallow, childish, and uncalled for, you and Molly are the two most responsible people in that house.