PSA for non-Greek Hellenic Polytheists:
Pssst! You know you can use the Greek names of the Greek gods, right? I'm not talking about ancient Greek. I'm talking about contemporary, spoken Greek. You know the names still exist in Greek. Right....?
Not only the ancient names for figures and terms have remained exactly the same for the most part, but also they're not worse, disrespectful, or "less formal". They are literally the Greek names of the gods/heroes/creatures/terminology today.
You don't have to address these figures the way our people did more than two thousand years ago. Millions of living Greeks today still speak the names of the Greek gods. In the Greek language.
I understand that the versions you use can depend on the resources available to you. And it's fine if you only know the ancient ones, or you only want to use those. But I'd like to make you aware that you don't have to be stuck in 300 BCE linguistically.
Not even the Greek language itself is stuck in 300 BCE! In fact, by 299 BCE, our language had already slightly changed from the year prior, and it continues to do so every year for... well, for a few thousand years at this point.
Ancient names make sense when one uses them in academic contexts, in the study of ancient Greek society and religion. But this religion and culture don't exist in a vacuum inside your history books. This linguistic stagnation in everyday life, though, is part of the centuries-long Western European / American obsession with seeing the Greek culture and language like something divorced from the real world.
There's no particular justification that demands you use the ancient versions in modern informal settings. On the contrary, why not address the Greek gods in the current form of the Greek language?
So if you want to use contemporary Greek, go wild. Use -ες ending instead of -αι. Go full iotacism. Use Έριδα not Έρις, Μοίρες not Μοίραι, Χάρη not Χάρις, Κάθαρση not Κάθαρσις. The differences are minuscule. And - let's be honest - you were not using ancient and modern Greek grammar (like the Greek cases, which depend on the sentence meaning) properly anyway.