We're 5'9" and fragile, 5'10", 6'2" and built like the proverbial brick shit house, and can get along fine in one *orthopedic quality* California King. Though I have heard much applause over at the poly forum on Reddit regarding the two Queens stuck together version.
I occasionally claim I married my husband for this bed, which he already owned when we started dating, and given my ortho issues I am not always entirely kidding. Usually my husband sleeps in the bed with me because it was in our wedding vows that he would keep my feet warm at night and thus this has been our tradition for several years now. The boyfriend sleeps with us when the kids aren't here or if we're traveling without them and in his room otherwise. If we're stuck with the two bed configuration while traveling, I sleep with the boyfriend because I don't often get much chance to and the husband enjoys his break from footwarmer duty.
Ultimately though they could sleep wherever they bloody well please; to quote Jayne (Firefly reference) I'll be in my (comfy orthopedic "huge tracts of BED!") bunk.