D.P.
Hi B.,
If your son is needing a booster with a cup holder, I would recommend Graco brand booster. They have one with cup holders to both sides and also has a back on it that comes up as your child grows taller with a place to put the seat belt in the correct position until your child is old enough and tall enough to be without the booster. If you get your son the Booster, then you can turn your daughter forward facing once she is 1 year old. My sons feet pushed against the back of the seat for a month or so. I would talk to your pediatrician about this. Mine said if he isn't uncomfortably pushing on the back seat, he should be fine. If she is uncomfortable and legs scrunched up, it may be time to turn her forward facing though. I had to turn my son around to forward at 11 months old though because he was really scrunched up and all.
D. P.