So my brother brought me a copy of Gauntlet so we could play together (as we usually do via LAN) and I can see from these forums that that's not an option, So;

We both download GOG Galaxy, have it running in the background. I host a game. There's no way for my brother to search, only do a 'Quick Join' which just hangs for him. The only way I would be able to get him directly in my game is by the 'Invite Friend' option and, funnily enough I can't add myself as a friend.

So in short, for anyone else looking for an answer to this question, it looks like you can only play with other GOG accounts.

well that's a bit misleading then

Yes, mp only works with gog Galaxy users. If your brother is in the same house, you can play on the same computer.

After reading this and other posts I think I will avoid this game. I have it on Steam but I want it drm free and actual offline LAN play.

AFAIK there was never an option for a LAN play for this game.