I would never invite a gang of dolphins into my house, I have kids.

Giant squid live deep under water. Housing one as a pet would require a tank half a kilometer tall! Dolphins should have large swimming areas but theirs can be relatively flat. And I could always buy from marineland now they’re finally shuttering. So dolphins

It’s not really an answer, but I’d be surprised if a giant squid could lift it’s tentacles at all without buoyancy to help.