a sentence:
His reign was much shorter than the reigns of both his father and his son.
to rewrite it:
His reign was much shorter than the reign of his father.
so, usually I write it :
His reign was much shorter than that of his father.
the following sentence is also acceptable:
Their reigns were much shorter than those of their ancestors.
in these cases, THAT agrees with REIGN, and THOSE with REIGNS.
a question comes:
can the first sentence be written as
His reign was much shorter than those of both his father and his son. ?
it is of course understandable, but the original form seems to be [than those reign of ], without an s, which is absolutely ungrammatical. what do yo think?