We traveled with our best friends this past October. My husband and his friend have been friends since the cradle - his wife and I have been friends since they first started dating (14 years ago) and our kids are stair stepped - 13, 10, 8, 5, 3 - and all get along great and are very nice to each other. My friend and I planned it out for over a year - we're both planners and handled everything. It went from a "Let's do a Halloween party and an ADR or two together" to "Halloween Party and 5 ADRs together!" and it was great. We all stayed at BLT in a 2 Bedroom that we always get anyway, so they just "rented" our second bedroom (translation: They paid for the Dining Plan and we paid for the room - great deal for all of us!).
We loved the time we spent as a big group (although that was only ADRs and the Halloween Party - when our costumes were dependent upon staying as a group) but we were very go with the flow. Sometimes we would disperse into random groups and go do separate things, sometimes we would split into guys and girls (fairly evenly matched at 5 and 4), most times we split off into our own families and smaller groups within the families.
I think if you try and do everything together, you would be miserable! We enjoyed the character meals we did together, but it was so much fun because we didn't care if someone wanted to go off and do their own thing. And we got a laugh about how some of the groups randomly ended up (for instance, out of our party of 9, only my husband's best friend and I were the ones who wanted to go on Tower of Terror - which was fine, I've actually known him longer than I've known my husband - so we left the chickens and went off to do that
).
Everyone had their must-dos, everyone had their own touring style, and surprisingly, there were very few times where we all had downtime in the hotel room together. It wouldn't have mattered if we were all in there at once, but we usually went back to the room earlier than they did (around noon) and they would get in late afternoon when we would be heading back to the parks or the pool, so we each had time to ourselves with just our families.
We actually loved it so much that we are planning to go back on an identical trip next year!