Best way of doing this is to get a group of 8 players with 4 players in each team. The two hosts will then search at the same time for King of The Hill. Whilst searching be sure to update the other host with what's going on in your lobby.
When it says creating match for both teams 9/10 you will be in the same game. Prior to searching you might want to make it so that you are all the same characters for both cog or swarm. This will make it easier to tell if you're in the same game or not, as you can't see the other teams names when picking the map. Another way to tell if you're in the same game is the same map selection and spotting icon.
If you don't get a map you want, then just back out and try again. Did this recently in a session and it took us a fair few tries to get Nexus to appear. When backing out there was a matchmaking penalty message that was appearing, but we didn't notice any difference.