I'm not a real firm believer in the cycle in a bottle.
If you want to spend the money on it, it's a risk. But fish flakes are the only proven method.
I also disagree wholeheartedly that you would reinforce three fish in there which need a 20 gallon tank.
It is a best case temporary senario. But it isn't how you should keep them. Each fish needs to be returned.
MABJ's iDevice used for this message :p
Well, I agree with MABJ that a 3g is really too small for even 3 harlequins. It's like keeping a betta in a bowl... people do it and they can survive, but they would be happier and healthier in a bigger aquarium. I just feel for you in that you're trying to help out your mom and don't want to let her down.
As for the cycle, I've personally used it but there's no guarantee.