The Drusillas rockhoppers were hatched at Edinburgh, are almost 20 years old and unlikely to breed therefore.
I disagree with your suggestion that Whipsnade relocated its rockhoppers to Edinburgh - they are actually a more prolific pair than any of the Edinburgh birds currently. As for gentoos - Whipsnade tried keeping them in 2009, I think they started with 0.4, whatever happened they didn't last long. Living coasts and Bristol both sent their gentoos northwards after they didn't cope well with the climate in southern england. I believe Belfast still have a few but their numbers seem to be dwindling and I've seen very little breeding recorded on ISIS over the years (which is why I was alarmed at Woburn's proposal to include gentoo penguins in its planned open-air walk-through exhibit....unless this was planned redevelopment of the sea lion area which I guess isn't on the cards now the sea lions are staying). As much as I don't like the setup, probably the best idea for keeping gentoo penguins in England is a temperature-controlled exhibit such as the one now at London Sea life.
I think the suggestion of moving the rockhoppers to Edinburgh is a good one, as if they are more regular breeders then that can stimulate the pairs at Edinburgh and also their youngsters may then have the possibility of breeding with the younger (or older) birds at Edinburgh. The larger the group the greater chance of success I would say.