As for the OP's original question, after a long number of years in full-time service, and especially Bethel service, a singe person can get his/her own room at HQ. Mark Sanderson, like Freddie Franz, would qualify. Also GB members, as we all know, get special perks—like going to heaven—so his own room is no problem!
As for personal info, he has an older sister name Kim who though raised in with Mark, did not stay in, going off to the "desires incidental to youth" early on. She was very cute in her early teen years and loved "the world." She ran around with wild, worldly boys. I heard she became a nurse. His mom died over 10 years ago, a kind thin woman, but evidently his pudgy dad Doug is still alive, though I'm not sure. Mark looks a lot like Doug but is even fatter now.
As a teen Mark was sort of organisationally nerdy, collecting old WTS publications, eager to talk about Charles Taze Russell, or excited about getting an original Emphatic Diaglott by Fowler and Wells (pre-WTS printer). If you would work in FS with him, he'd talk about how the heavenly inheritance was the more glorious destiny. Back then he seemed like a WTS romantic. I have an old contact in San Diego who has related some of this to me.
Mark never partook of the memorial emblems while in San Diego, but as soon as he finished high school, he left for Canada to pioneer. Then he lost no time in partaking there at 18 years old. It caused some controversy in the local congregation as you can imagine.
A "company man" indeed: "the senior brass have yielded Sanderson unusual latitude in some strategic areas of organisational command." It is typical of the older GB members to let the younger members among them basically run the show. Look at how Ted Jaracz, then the youngest GB member, took over things back in the early 1980s. Now it is the two youngest ones, Sanderson and Jackson who are setting the pace.
Likely the old guard are tired, and in their eyes the younger members represent the org's future.