I have no idea how to pull it off, but my Zero muse pinged this like nobody's business. He wants his trifecta of favorite people in the same house. Zero very rarely voices his desires but he's going through a very SELFISH stage right now. If Zero thought he was lonely living alone and wanted somewhere to stay...he'd snatch him up.
I don't remember...does Hikaru even KNOW Zero is a vampire? If he does, it was from way back when Ichiru was here and Ichiru told him...
If he moved in he'd live in a 4 bedroom house in sector 4 with Zero, Yuuki and Yuuri.