"Ancient Greek Religion & Lore" and "Ancient Roman Religion & Lore" are separate fandom canonicals. One of these is two orders of magnitude more popular than the other one and I'd bet on there being a lot of overlap, precisely because so much of the commonly known canon for the first is via Ovid and other Roman writers. For tagset purposes I agree with separating them, or anyway with making the attempt to; Romulus and Remus would have to move to Roman, and it might be worth duplicating a bunch of the others under their Latin names (for example, Ares would have to stay in Greek but Mars could be added to Roman), but those are the only two that are definitely not Greek.