Expect 20-25% of the FW GVWR to be on the pin. This amount of payload on a SRW truck once you have your family loaded in the cab will most likely exceed your truck's GVWR before it exceeds the GCWR.
You may also find the your RAWR may be exceeded. There are ways around this since the axle and frame have a higher rating in the SRW than what is posted. Going with higher rated springs and 19.5" wheels can allow you more payload.
I carried a truck camper on the back of my F250 that resulted in a 7000 lb RAW. Once I hitched up my enclosed trailer, I was closer to 8000 lbs RAW. Going with suspension modifications, 4500 lb rated rims and 4805 lb rated tires, I was able to confidently and safely drag this 19K lb GCW combination around easily across the western mountains and half way across the country.
I would still be using this setup if I was not planning on a truck camper 1.5x the weight of my current one. With the exception of some Canadian provinces, the listed ratings on your truck door opening are warranty limitations. In many states you register your truck for the GVWR you want and the only legal restrictions are your wheel, road bed and stopping limits.
Only you have to decide whether you will scale back your FW purchase, upgrade your current truck or replace your current truck.