Welcome, coolhandluke!
To further clarify, Germany may move out of the sea zone in combat movement even if its ships end up in a friendly sea zone. Moving to avoid combat in this situation is considered a valid combat move.
I know that it is impossible to do a combined allies assault, but I have an interesting predicament.
Britain attacked Germany’s fleet in space 6. Germany lost the TRN and DD, but they chose to submerge their 2 SUBs. Now their is a British BB, DD, TRN, and SUB in that zone and two German SUBs. It is russia’s turn and they decide to take their sub and attack Germany’s SUBs. I know that the british ships cannot help attack in this battle, but can they take hits for the sub. Can I turn my battleship on the side so that it can absorb a hit for Russia?
nope
You may defend together but never attack since the UK ships are not “placed on the battleboard” they can take no hits.