actually, its OK if they split, since the result that they'll spread slightly as two cards after you take them which is what its supposed to look, you're holding 2 cards. If its a triple, you need to be more careful. Try pushing down with the right thumb.
. The idea is to appear as if you're taking cards with your LEFT thumb, NOT pushing cards with your right thumb and taking cards. ( this is if you take the cards into a dealing grip). The reason you push is to make taking two cards with the left thumb possible.
If re-read Card College's description with this in mind, as important as it is its mentioned very briefly.