You'll have to adopt out the Tinfoil's and an Oscar, if upgrading the 55 is out of the question. A 6' 125 would be the minimum size for 2 adult Oscars.
I've never heard of a Rocket filter (no input on that). Oscars are big messy fish and require a lot of filtration and and big water changes. A sump is always a good bet, big canister filters (Fluvals or Eheims) expensive but good, The Filstar XPXL is a great filter approx $180. Aquaclear 110's are great HOB filters but you would require a few of them with Oscars.
With Oscars you can never have too much filtration.