Not participating, however, you should make 10 tie maps right now. if any of them are played during the regular match, then those are dropped from the 10.
I'm telling you this will be a problem.
Each team should pick 5 tie maps ranked 1-5, 1 being their most desired. The two teams should paste their top 5 in chat. The maps that both teams have suggested will be the map.
Of course there may not be a tie for each teams 1st pick, so it would go by highest average, if team A had map 1: xbmap and team B has their #2 map as xbmap then that one will be played.
Of course if 2 teams can pick one without fighting, then let them.
Or have them take turns eliminating maps from the map pool until there is one left; The team who has the most points for after 2 maps will get first ban.
EDIT: thought this was for a tournament, this doesn't much apply for regular play.