It's the luck of the draw, unfortunately. We can't expect everything to happen as we'd like it.
I've got two grandchildren from each of my children. I'm very close to my son....his two children are very influenced by their nasty mother , and frankly I don't feel overly happy when I'm with them.
My daughter and I have a fraught relationship - just too different I'm afraid. But her children are the cream in my coffee, I adore them and would walk over hot coals to spend time with them. And ironically, this intense love for the GC has improved my relationship with my daughter, too. At last we have something in common - these two lovely children.
I guess what I'm saying is, there is no guarantee that the children from the "difficult" adult child, will also be difficult. And the children from the "favoured' adult child can end up being difficult .
All we can do, is take what fortune doles out to us, and be grateful . Many "grans" are not so lucky.