Pigless....i have felt this way for a long time. DNA is just that. I adopted most of my kids.
If we dont resonate in a positive way with somebody or they dont resonate in a positive way with us, I am okay these days with just letting it go. Often how they feel about us is more about their issues than ours.
I like the saying "what you think of me is none of my business."
Family to me is who loves you and whom you love and can be with in a calm and positive way, rather than DNA. I really believe this.
It is not about how kind you are. Not all people appreciate kindness...they may even twist it into something else. All we can do is our best then let it go.
I am sorry for Ferb, if indeed a stronger relationship would have helped him. But relationships start at the top usually and are intertwined. If Mark doesnt speak nicely of you, it is normal for the kids to be withheld and to pick up the vibe. I dont know my sisters kids. One married yesterday. It was just another day to me. She doesnt know my kids. When Jumper marries, Sis wont be invited because Jumper doesnt know her. Its okay.
I am so sorry this saddens you. And I am sorry you dont have the relationship you want with everyone. But I feel your thinking is correct. Have a nice day! 
