Unable to join party members in grog beach

I am getting an error message that the spots are reserved for other players when trying to join a party in grog beach. They are levels 15 and 16 and I am level 25. I am playing on an apple iPad, everything is updated to the current so, and the game is updated, I am not jail broken, and I am running off of wifi in my house. My inventory is not full, I have tried just going to grog beach and they are not there. I am in the party, but am unable to join the other party members. There are no other players on the level with my party. I have logged out and back in, and am still unable to join them.

First, welcome to the forums. Enjoy your stay. :)
Second, there is a command ( /partyinvite 000 ) that prohibits anyone from joining that persons session. That may be the problem, if it is still occurring please contact support at Support(@)Spacetimestudios.com.

there's also the chance that they have others along with them, a PuG. then the game is counted as FULL.