Put them in a single deep. Then feed 1-1 syrup. And feed and feed. Don't bother with 2 boxes, just make sure they have a single deep full. They can make it (assuming as Kathy said, they are a decent size swarm)
If you have the equipment, what do you have to lose? $20 of sugar? And if they don't make it you end up with a box of drawn comb.
That's worth $20 next spring when you hive a different swarm in it, if they don't make it.