Avoid the half ton 5ers. They are actually a net loss of space in order to keep weight down enough to be half ton towable.
As mentioned previously, the 26-28 foot range will be your safe max with a half ton. I have a 27' Cougar that weighs about 7500 all up with full water, fuel, food and drink, plus personals--and I go solo. Add in the stuff you'll have with a wife and 3 kids, and the weight will climb. While my 1500 with tow package and 3.92s was rated on paper at just shy of 12k, I didn't like that I knew it was behind me- I am a lot more comfortable pulling it with my 2500. Not to say it was unsafe; I just prefer having more truck to pull it.
Look at bunkhouse designs, especially since your kids are young (hence small). Storage in any bumper pull will be well less than you'd have in a 5er, but usable floorspace will be greater. You might find a half ton TT with dual slides but you'll probably be better off with a single super slide, which will generally have your dinette and chairs/couch.
Bear in mind when brand shopping that 90% of all rvs are made by the same factories in Indiana, and no matter how good the pictures make them look and the brochures make them sound, they are still built ******. You WILL be fixing ****, especially since you're planning to live in it for a while. Can't very well turn it in for warranty work when the whole family is living in it.
Sucks that you lost your stuff in the fire, but happy to know you all got away safe. Hit me up if you have more trailer questions--I'm no guru, but I research a lot of info for my own use, and will freely pass it on if I can help.
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