i'd let them hang out there for a few days to a week, let them get used to their surroundings and, if they weren't tankmates at the store, let them bond as a school. if you let them get street-smart and acting cohesively as a group they'll be much less stressed at a big scary betta in their realm.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)