Welcome to the board! I am posting some links in case you have not already discovered them. Are you set on Montego Bay or are you open to other Jamaican locations? As you will have 6 adults, it might be best to look at villas if you all want to be in the same unit. If you are okay with 3 separate adjoining rooms, you options will increase. Most of the people on this board are pretty much addicted to Negril (as am I) and have been to Jamaica numerous times with and without families of all ages. There are quite a few all inclusives in Negril (such as RIU, Grand Pineapple, etc) but most rooms would only accomodate 2-3 adults. If you open to accomodations that only include breakfast, some suggestions in Negril would be CocoLaPalm, Country County or Negril Tree House. One of the joys for many Negril visitors is checking out the numerous restaurants in town with a wide variety of both Jamaican and international cuisine and a wide variety of costs.
You miight also want to repost your original message in the Negril forum which is more widely read and you will receive many more replies.
There are lots of exciting tours to take - everything from waterfall climbing, zip lines, river rafting etc. Do you know what dates you are looking at - the low season generally runs from April 15 to December 15 when accomodation prices are considerably lower than high season.