[Endoperez]

About multiplayer:

if all the players don't have the same version of the game (version number, demo/full doesn't matter), battles will be shown differently. The battle overview (units/commanders/... lost) always shows tells what actually happened.

Multiplayergames can be played with demo/full version games, but unfortunately demo hasn't been updated in ages. Because of that, you have to find a patch older than the newest. For at least some time the newest demo had a severe bug that made Utgard theme of Jotunheim dramatically different from what it was supposed to be. I don't remember if the demo has been patched to 2.11 or newer, which would have corrected this bug.