Sorry for late reply, but have hope it will be useful - multiplayer in Two Worlds 1 is working fine. The trick is, that after installing it, game will have a couple of different shortcuts in start menu (attached screenshot). The one which is useful for MP is "network play", after launching it, you should be able to create MP account and be able to play online.
I've tried by myself and it all seems to work fine. But only if I'm launching game through this shortcut.
Thanks! I actually own the game on Steam, not here, so sadly I don't have that shortcut, and the devs don't respond in the Steam forums. I'll try it later again out of curiousity, as someon was saying on the Steam forums it works again, but for me only TW2 works. I asked here as well since the MP was cross-platform, so I was interested if at least the GOG version works.