This might be a silly questions since this variant is usually a friendly game but I was wondering if you are allowed to coordinate plots with your partner? When we played, during the plot phase each team kind of looked at each other's plot decks and they both chose plots together. So, stark for example can notify their ally if they are playing valar morghulis without having to let their opponents know. Only seems fair.

I am assuming this is allowed since you can coordinate with your allies and "send Ravens." To each other. And it is an equal advantage on both sides.

Generally, hidden information is supposed to stay hidden. It's not really Thrones any more if people, even your partner, know what's in your hand, plot deck, etc. So personally, I'd say coordination by discussion or table-talk is fine, but showing your cards to each other and saying, "I'll play this, you play that" really isn't. Even the best of allies doesn't know everything the other can or will do.

That said, it's a variant rules game. So long as everyone at the table agrees on the rules being used, I'd say you're good to go.