As far as bonding, maybe her father taking her out by themselves might work. That way it's just the two of them and she can focus on him. In some cities, there are "Daddy and Me" classes that she can do with him. Maybe going to the park or something like that would work too. I know on days my daughter tries to avoid her father, I will just leave and go out for a bit so she is left with only him around. Same goes for when she seeks only him, he will leave for a bit so she has only me around. This has worked for us quite successfully After one of us is gone, we will typically find her favorite toys and set them out and we will start to play with them so she will come to us. Usually within 10-15 minutes, she will. After that, she is fine

Yes, it is true that sensory seekers will hit or pinch to gain sensory input. My 2 year old is notorious for this. Especially when it is myself and my 4 year old. She fill find us just to hit, pinch, or bite. Honestly, I am still trying to figure out ways for her not to use my 4 year old and myself as her stims. She has been working with her OT with that issue. It has decreased, but she still will do it quite a bit (Like 1-2 times a day for each of us) So if your daughter has a OT, talk to them about her using your son as a stim and they can figure out some outlets for her to use instead of him. It does take time though.