Its pretty simple tho requires decent java knowledge, all you have to do is pick 1 login from the 2 lets say l2j high5. And rework the tauti projects loginserver on the gameserver side for the l2j login. That way the loginserver will be able to hook both gameserver and than you just register 2 different hexId and run it as usual.
PS.: you might also need to rework the mmocore the same way but im not sure about that.