No, the ability to create custom parties is not
really available at the moment. Then again, this is EA. If you want to play with most/all features implemented, you might have to wait until full release.
Larian said they plan to let players create a full party (in a
Reddit AMA, and possibly elsewhere). As to whether this is still true, who knows ? Larian made other announcements that turned out to be false, and never notified us of it.
Now, there is a
work around. If you launch 4 instances of the game (through the .exe file, not the launcher, and setting the graphic settings to lowest), you can create a multiplayer game with one instance and have the other 3 instances join that game. This is how people do a custom party at the moment.
