which TT is the best to downsize?

I would defnitely stick with a bunkhouse while your kids are camping with you. I like this one: Coachmen Apex 235bhs. It's lightweight (4293 lb. dry/6500 gvw), and it's only 26'7" from bumper to tongue. The large u-dinette is spacious and can easily be converted to extra sleeping space when friends of your kids come along.

Here's one a bit longer that also has a couch in addition to the u-dinette (29.5 ft. total length/ 4767 lb. dry/7000 gvw): Coachmen Apex 268bhs.