Baby sissy

I don't know how to feel about this

But I have a 3 month old little girl and her brother (6 years old) from a different mom don't want nothing to do with her, like he'll tell use that she's crying and that's it, he won't want to touch her or be near or around her or just do anything with her, but my nephews 4,8,10 years old love having her around and play with her and the 4 year old loves giving her kisses and holding her and just do things with her, and then a friend of mine, her little girl(1 years old) likes having her around she'll touch her and play with her toes and try to give my her things and I don't know how to feel about that like the other childrens love having her around but her own brother doesn't want anything to do with her...How should I feel about this?