There are three boxes. Young men, two grandsons carry two of them.
The third box is carried by two of the sons-in-law, together. And even together, these are heavy boxes. Old (well, thirtysomething and fortysomething) men know their limitations, and know to protect their backs.
The young might not have learned this lesson yet. Or maybe they’re just stronger!
(See also: Posts That Might Be)