When my husband or I port into a battle (usually because the "join combat" button does absolutely nothing) our characters are invisible. That is to say, he comes into my fight, with crew. I see his crew. I see his name. I don't see his character. It's a little disconcerting to have an empty spot cast a spell.
By the same token, if I join his battles, he claims he sees my sword attacking when I crit, but not my character making the attack. If we stay on each other's ship, our character is still invisible (but the first mate is right there). The only way to become visible again is to zip out to a life fountain and port back when our partner isn't in battle.
Also, why can we not unbottle our ship that we bottled to join the battle? Again we have to port away and teleport back to unbottle our ship again. Is this a bug or a feature?