Scenario crashes in multiplayer

I wanted to make a 1v4 scenario where my brother (who is very good) went up against me and my three friends (who aren't very good). I made the map and put everything that I wanted in, and I playtested the scenario multiple times, but when I went to play it online it froze and wouldn't unfreeze. I kept trying, I made small changes in the player data and looked for any way to solve the problem and I couldn't find anything. I even played a scenario that I made a long time ago in multiplayer, and it worked just fine. I just can't seem to get this to work. Can anybody help?