Let me also take a shot in the dark on if manual invites could be sent out and say that the person initially mentioned in this bug would really like an invite to the playtest for their account here
Description:
When inviting another user in your steam family to the deadlock playtest if that user then plays a family shared copy of the playtest the title's in game invite menu marks them as having "Already Joined" despite them not receiving or accepting an email invitation. The invited player...