...I think you may have ruled out one option (TT) too soon.
If I was traveling with 4 children, there is only one way I would even consider RVing - A good size TT with a quad bunkhouse, and a 1 ton full size van (preferably a V10 Ford E350) for towing it. Gives you plenty of room for everyone when on the road, and an RV that gives everyone their own individual sleeping space. Something you will NOT get with that many children, in just about any Class A motorhome. A 5er could be had with plenty of room for everyone, but like you said, cramming 4 children and 2 adults in a crew cab pickup would not make for much fun on long trips.
We have two children, and traveled in a similar fashion for many, many years - a 34' bunkhouse TT and Ford Excursion tow vehicle. Worked great, we traveled all over the place in that rig, sometimes still miss it. Eventually ('bout 2 years ago) we traded up to a Class A (Georgetown 351ds - see signature). Works great for us and very glad we moved up to the A, but we only have two children. If we had 4, I almost certainly would have stayed with the TT.
Only motorhome I'd be happy in with that many people would be a custom built bus conversion built with enough sleeping space for everyone. However, that just ain't going to happen in this lifetime for a working stiff like me thats not independently wealthy. Soooo, like I said, if we had 4 children, we'd have stuck with the large SUV (or conversion van like I mentioned) and quad bunkhouse TT.
Thats my story/recommendation, and I'm sticking to it. :)
