can flowerhorns be kept in groups

Anything can be done, but in this case there are a lot of reasons to hedge that bet. The parent species of flowerhorns are not known for being particularly easy to keep with others. How much space is an issue, changes with maturity, and if a pair decides to try to breed all bets are off for the rest of the fish. As a blanket statement there are lots of reasons it would fail if I simply said sure it can be done.

For example, something 3 gallons can be called an aquarium, so in that case of course not.
 
can I keep more than one fh in the same aquarium?
I kept 4 females together awhile back, but that's not saying what works for me will work for you. As hybrids from who-knows-what-species, they an be as different as apples and oranges. If it were up to me I would aim for a group of females that were raised together
 
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