How do allies work in this game? I am trying to see if I can play hotseat with my brother as allies in an offline scenario, but I can't tell how to be allies. Different maps seem to allow different races and colour choices. Are you an ally if you're the same race? Or the same colour? How does it work? What is a good map for freedom of choice if there is one as far as races & alliance goes?

Thanks in advance for any help

You have to select specific maps, that say (allied) next to their name.
You can see on the banner to the right of the player names, which players are allied. Just have you and your brother be the players that are allied.
Colours and race don't matter (tell that to BLM, lol). You wont be the same colour as your ally and you can be a different race.