We split up the kids all the time, it is good for them. There are weekends where I take the girls for girls weekend out and my ex does some male bonding. I think they just sit around and watch TV but it makes my kids happy, ya know?
So let the daughter have her mom time and just keep his son all weekend. Win win.
So far as the upcoming hearing goes the only thing that could hurt you is not making decisions that are best for the kids.