In attempting to join a PC's party, I've found that I can't. I believe we've both added each other as friendlies on our IFFs, but it always shows the other as being unable to add to party. Is this feature disabled, bugged, or am I missing something I haven't done yet?

Its been removed as part of the combat stuff. I believe the only way now is when one player is unnconcious and is added to another players party to move them to a bacta tank.

Or arrest them.

The arrest one doesn't work, despite having tried on a few different occasions. I haven't tried with an unconscious player yet.

“The arrest one doesn't work, despite having tried on a few different occasions. I haven't tried with an unconscious player yet. ”

You can add someone to your party if they are arrested. Just tried it out. They don't appear "arrested" when you party with them, but if you look at the scanner, they remain arrested.

Zero that was in reference to receiving the achievement. >_>