Han can totally barter or gamble to win slaves. There aren't any set in stone ways for this to happen, so you can do it however you'd like. Some owners would like the thrill of gambling, the slaves are just property. You can still hash it out with slaves' players though.

Crew can bring slaves back to the ship with them, as long as they aren't pursued, and the captains would let them send the slaves off in their transporters or crew's ships. The only way they'd stay on the ship permanently is if a player apped in a Thisavrou OC.