At the moment when trying to launch a 4v4 battle with friends the only solution to find a 4v4 compatible map is to select a map in the battle lobby and place the mouse cursor on the Start Battle button to check if there is a red message saying that map does not allow that number of players.
Moreover strangely the number of armies restriction does not exist when doing a battle with me and 7 AIs. It is perfectly possible to start a 4v4 battle with one player army + 7 AI armies on a map that would not allow 8 player armies...
I don't know if there's a mod helping for that, I've taken a look but did not find anything so far.
Does someone know of a list of the Vanilla maps with info on allowed players count ?
Thank you in advance and good games !