I asked a friend in the know about fish.
‘sentani is endangered in nature because of introduced species.
But this and all the others aren’t difficult to find in the trade, because they’re so easy to breed. Hope they have a big tank, apart from parva they’ll all grow to 12cm.
I’d make sure it’s very well oxygenated, as these are very lively fish and will not tolerate low levels. They’re also very greedy, so will eat just about as much as you throw in.
So feed moderately, lots of o2
and monitor nitrate etc. I think they’ll need lots of fast growth for export. Hornwort is good for rainbow tanks because it likes the water parameters.
If these fish do prefer harder water I’d mix Your top ups with a bit of tap too.
If it makes you feel any better I think Walstad kept some if her best tanks with rainbows.