@Bad Wolf, I don't think we are disagreeing.
MBCs have some latitude here. It it's obvious the scout planned or completed the activity according to the requirements it should be immaterial who went along for the trek, as long as the requirements were met.
I think that is the test. If it counts for the merit badge, it counts for the award. For the Hiking merit badge, they need to prepare a hike plan and do the hike for it to count. It doesn't matter who they do it with. For the Backpacking merit badge they have to "participate" in the three 3 day 15 mile treks and write a plan for and then do the 5 day 30 mile hike. Again, it doesn't matter who they do it with. For those badges, I accept hikes and treks done with family or other groups because the requirements don't say it has to be done through scouting. I have a scout going on a 4 day backpacking trip with his Eagle Scout Uncle in Alaska this summer -- you can bet I"m giving him credit for that for the Backpacking Merit Badge.
Outside of the merit badge context, nothing done with family counts. My son and I could backpack the entire AT next summer and that wouldn't count toward the award. I guess that makes sense because it forces scout programs to become more outdoor oriented (you want the award, you plan outdoor activities that count toward the award). Fortunately, as a troop, we camp 12+ nights a year (not including summer camp), hike 5 to 8 miles on most campouts, have monthly bike rides or hikes, try to schedule two 15 mile backpacking treks and one thirty plus mile trek and do at least one float trip.