Yes you may bring your children, make sure you include them in your RSVP.
Yes, everyone is welcome to bring their significant other or a friend.
Dublin airport is often the easiest and cheapest though it is farther from our destination. There is a train available from Dublin to Portrush which is about 4-5 hours. Belfast airport is closer to our location at Dunluce castle. If you wish to have a rental car they may need to be reserved earlier to get an automatic. Dublin is a 3 hour car drive from Portrush. Belfast is a 1 hour drive from Portrush.
There is not a room block or discount. The Elephant Rock Hotel and Bushmills Inn were recommended to us by our wedding planner. You are welcome to stay at any hotel in the area.