First off, welcome to the game! It's addictive fun and many of us have been here for years, and years.....
Sadly you cannot have a multiplayer game with more than four players at once, just as in real life. So yes, splitting into two groups may be your best option.
You can also create a country club and invite your friends to join. That way you can create tournaments that you can all play, although you would all be playing singly as WGT is not set up to allow multiplayer in club tournaments.