I think the answer is
I give fives, but sometimes twos,
Poker hands are composed of five cards and players are dealt five cards in the classic five card stud version. However, the most popular version of poker is Texas Hold'em where players are initially dealt two cards (with the idea of forming a five card hand with other cards on the table).
If you've got two and seven, you'll probably lose.
In Texas Hold'em the statistically weakest hand is an unsuited 2 and 7.
If you bring me nothing, you won't be allowed in,
You need to pay money into the pot in order to play any hand.
you'll leave with nothing if you don't win.
All money goes to the winner of a hand.
You want to get them all in a line,
This refers to a straight (a run of five cards in numerical order).
or all matching houses, that'd be divine.
I think this refers to a full house, a hand with a three of a kind coupled with a pair.