Hey XT-19, welcome to the forums!
I've only ever tried multiplayer against one other person at a time, so I can't say that i've not encountered this problem before because I haven't tried. I've not heard of other people mentioning it before though.
The only thing I can think of is that you need to check whether you all have the
exact same game files; any differences, no matter how minor those differences are, could cause the game to crash. The best way to do this is to make sure you all have the most up-to-date version of the game by forcing an update. That way, you'll all have the latest version of the game, and get rid of any game modifications that might interefere with the multiplayer. If you all click on the options menu, then click on the updater tab, you'll see an update option in the screen that then displays.
I've mentioned this as the most likely cause because it's entirely possible that someones game is trying to download an update when multiplayer is initiated which is causing a freeze, or someone hasn't performed an update yet, or even has modded their game files but hasn't told the others and passed on the modded files so the game crashes because their files are different to those that the other players are using.
I haven't got any other suggestions at the moment, but i'll try and contact Mike (The developer) and see if he has any suggestions that can help. He's absolutely swamped with his job at the moment though so it might take a while to get a response. I'm sorry that your first multiplayer experience results in problems, but i'm sure we'll be able to sort out a fix before long if you're willing to wait.
_________________"Anyone without a sense of humour is truly at the mercy of the rest of us."