If both the same rate see if your dp can get a 0% transfer first.
If so i would transfer their balance to 0% and pay yours off with the cash, then put down payment of theirs and try and hit it over the next few months.
Citibank, virgin, suncorp and anz all have had balance transfers in the past

Edit: if they can't get transfer then hit highest card first ( or put half on each and reduce your limit )