You should decide camber or rocker or hybrid.
If there's a lot of ice where you ride or if they are fast and carvy in their style the camber, eg burton protest is Burton's top kids board. Or maybe a burton process in camber - adult board.
If they want something more skatey burton custom smalls is Flying V, fun to ride, not as good edge hold, more forgiving.
The 105 lb kid should almost certainly be on a kids board, the bigger kid could go either way.
I'd also look to the used market.