Both nouns are tricky here.
"Hell" might be
Acheruns
Avernus
Inferi
Infernus
The trouble with hero is that it is a Greek word imperfectly assimilated into Latin. Here we need (I think), a dative plural. Heroibus is not our only choice, but I think it's the best.
I can't really help with the choice of hell-word. It depends a little on how you envision hell, and a lot on what it is you're trying to say. Just to set the forms down:
Acheruns heroibus est.
Avernus heroibus est.
Inferi heroibus sunt.
Infernus heroibus est.
Hope this helps.