I agree that family costumes are always a hit. I think Captain Hook and "Lady Smee" could be cute. Or maybe mum & dad could go to Pirates League too
I would check a few sites with party break downs. We used Disney Tourist Blog and Kenny the Pirate's party resources before our last trip. From there make a list of priorities for you and your family - you know better than us what you will love (though I do suggest fitting in the Boo To You Parade at least once and Hallowishes). We used our priorities to make a rough plan and with that we managed to see the parade, fireworks, stage shows, get all the magic shots, do a little bit of trick or treating and we also met lots of 'rare' characters. Including Jack and Sally, The 7 Dwarfs, Jack Sparrow, Maleficent, Aladdin & Abu, Donald and Daisy (we were dressed as Heuy, Duey and Leuie so that was a must for us) and several others that don't spring to mind right now and that was on Halloween Night when the park is super busy! Though, we didn't ride any rides or do anything available during 'regular hours' because we thought that was a waste of party time.
Point is, going in with an idea of what we wanted to see/do ahead of time really helped us be able to check off lots of stuff because we didn't spend a lot of time hanging around wondering what to do next. We decided in each queue where we'd be going next and headed straight there. With two young boys you may not want to dart around everywhere like we did, but make sure to spend a little time researching the party so you have some idea of what you want to achieve - since there is only five hours part time you may as well try to maximise that any way you can!
Hope you have an amazing party!!