Whoever you booked with has notified Couples of the reservation. When you get to the airport in Montego Bay, the folks at the Couples Lounge will have your name and which resort you are going to. No problem, mon.
No you do not need to contact them with your flights. The lounge is always manned and the shuttles run about every 20 mins or so. Last year we did the same thing and it never occured to me to let them know what time our flight got in but when we were about 5 steps away from the entrance to the lounge we got a big smile and then a welcome home. Ahhhhhhhhhhhhhh the door way to heaven.