Hi twobytwo and welcome to Cruise-Chat.
I suspect your friends who live in Tallinn would know the best place to meet, and whether they're allowed into the port area. We once met friends in Stockholm, who were waiting for us as we walked down the gangway from the ship. But this was pre-Sept. 11, and I don't know the regulations at various ports now.
Could your friends find out if they're allowed to meet the ship? Otherwise, perhaps they could suggest a meeting place right outside the port area where you could meet.