Whats size are your tank at home? What size is your dad's? What are they currently stocked with?
I would still just keep the cons, even then a 20 could be cramped once they get 3-4"
Your call though, if you do frequent small water changes, make sure the nitrates are below 20 ppm, and there are no agression problems in the short term you may make it a few months before that RD flips the aggro switch and kills the O and Cons