Why is my stepmom obsessing about feeding my brother?

she feels empowered because she can feed and it's working for her....that's great, to a point. When you start obsessing and insulting other moms who don't feed that is when it's gone too far....talk to her and tell her that you don't want to hear about feeding and it embarres you to go out with her because she insults other moms who don't. Then tell her you want to stay home until she can learn to control herself.