It's JinxedMinx's game of course, but I feel allowing non-Olympians is a big mistake with this particular game.
Other pantheons really add nothing significant to the character dynamics, and in fact I believe they seriously detract from the best aspects of what could be a really great 'family spat' type of drama.
Greco-Roman deities fill any and every concept or archetype anyway, usually with multiple options.
Throwing in the random Norse, Celtic, Egyptian, Babylonian, etc, etc... god seriously disrupts the charming flavor that drew me to this idea.
Edit: and it's not like we need more players - even without the non-Greeks, this is shaping up to be a pretty big game.