An Elite brand stingray filter is a good bet for a cheap, quiet filter. I use them and they are dead silent (there is an initial 15 minutes of light noise as the filter gets started). Mollies do get big, so stick to 2. I don't know about molly aggression. Always ask the store what the salt content of the molly tank is. They are a brackish fish (brackish is the border between salt and fresh water) and may need some time to get used to fresh water if the store keeps them salted.