3,4hr legs. Max 7hrs in a day with wife only. 2,3 hr legs, max 4hr in a day with kids (8,6 yr).
I do not allow for food or drinks in the cockpit, so we need to stop to eat, so our leg timing works out.
Unless they have genuine interest in flying, you need to keep them comfy and entertained. My kids are growing some interest in piloting ever since I let them sit in the front seat, but that doesnt translate into patience during long XC. Wife has clearly spoken that she actually doesn't enjoy flying GA but she acknowledges that it does save a lot on the door2door block time compared to airlines or driving when traveling to many destinations, so she is "happy to tolerate it".
Get your dynamic prop balancing done. My wife noticed it once I got my AP and bought the machine and took a half day to bring it down to quasi 0. Her daily tolerance rose from 3hrs to 8hrs. But she doesn't like driving more that 6,7 hrs anyway, so that's our cap.
Stay above turbulence even if that means higher headwinds.
The Bluetooth connection into noise canceling headsets combined with panel USB power allows for wife's Netflix binge. Kids have their tablets with headsets. I assume getting starlink could further improve the situation.