Ania:
I think if your dd is willing to skip, you should let her.
Even if she is "just" in the top 3-5 percent, she is probably bored with her classes and ready to move on. I subject-accelerated in jr high (20+ years ago) and really liked getting out of that scene faster!
I think this decision should not depend at all on what DS is doing. If DS doesn't want to grade skip, I would encourage him to subject accelerate in his areas of greatest interest. He will still get to see his friend and girls his age every day.
Good luck!
BK
