Here's a thought: If you build the beds up higher (4 feet, to 6 feet above the floor) all that space UNDER is cabinetry, and highly usable. Master above in the front, with galley to one side, Kids near on the other side. Remember: If you are making this for habitation, you HAVE to have escape hatches next to the beds. One in the vent hatch for your bed, and one next to the kids bed, if they aren't next to a door that they can just bomb out of in an emergency (fire). You HAVE to put this in no matter what.
Secondly, unless you put the galley outside in a shelter, you may have to have a window and fire extinguisher at the cook stove.
Finally, consider how you will heat the rig, since there will be poor ventilation in a cargo trailer, and propane powered catalytics can kill kids faster than adults.
One set up I saw had a small air-tight stove, with air supply piped in through the floor, and smoke stack out the top. Worked great. Fire alarm and CO detector right next to the stove.
Remember that you will have to pull everything (toys and tools) out before anyone can cook or sleep. You cannot just load to allow simultaneous use, since your load distribution will be wrong if you are taking heavy gear like ATVs or snowmobiles, gen set,cans of fuel, pioneering tools, etc.
Be sure to take chains and locks for all the stuff.
One of our guys comes to elk camp each year set up like you describe. He hauls tons of stuff, but once the trailer is empty, just cots, a heater, three ice chests and a small library. Oh, and their bags of clothes. Everything else is outside. Locked up.
I noticed in another camp, that the wives (family elk camp) had fixed up the Forest Service pit toilet with several selections of baby wipes, and hand sanitizers, and bottled water. and Air freshener. Lovely.
Good luck, have fun.