My two new fish.

Question
Okay, so my friend asked me to rescue two black tetras from his roommate who didn't bother to take care of them at all.  They were the only two left that hadn't died and you couldn't see anything in the tank for how dirty it was.  Now, I already have some fish.  I have two male guppies and an otoclinus in a 6.3 litre tank.  The tetras are sitting in a small fishbowl now that I nabbed from my friends house.  However, I worry about the porr guys not being in an oxygenated tank.  Can I put them in the tank with the others, or will they need a separate tank?  I also have a quick question about my guppies.  I know you're supposed to get them a slew of females to keep them occupied, but honestly I'm poor and I don't want them to breed anyway.  The two male seem to get along really well too.  Will this change in the future if there are no females in the tank, or can they stay together in there as they are now?

Answer
So glad to hear this story had a happy ending! Thank you for your care and concern, withour your efforts these fish would have almost certainly been goners. I wish everyone could be so conscientious an aquarist. Enjoy the holiday and feel free to write back anytime.