is the SKS more accurate and does it have a bit more velocity due to the longer barrel??
Yes and yes, but not to such a degree in either case that it would matter.
Unless one is looking at a Dragunov variant, you don't buy commie rifles for accuracy - but for reliability.
Fps (velocity) loss or gain from changes in barrel length usually only amount to 10-50 fps per inch of difference. 50 being a hell of a lot, and very unusual. Each gun is different, so you can easily have two identicle guns that shoot the same ammo at measurably different speeds. Same for accuracy.
Just tell your pops to buy them both, that way he won't regret not having the one he didn't get.
