About the use of complementizers like whose

i saw a post online and it was about a sentence being grammatical or not.

here is the sentence

The old man loves him no less than the oldest, after whose death he becomes even more attached to the younger as if he is a solace from god.

and here is what i think

which, whose, where and that all are complementizer (sorry that i have mispelled it), and they cannot be assigned a preposition with no good reason at all. the preposition needs to be either the modifer of a noun phrase or a modifier of the complementiser. but in this case, it is only an adverbial of time. it doesnt not really work that way.

i think it will be better if paraphrase it to be sth like the old man loves him no less than the oldest whose death later becomes the main factor of his gradually increased attachment to his younger son........blah blah blah..
that would seem more natural than messing up the preposition and complemtizer together.