美人薄命とはいうけれど。ということは、内のかみさんは長生きだな。

。、。

They say beautiful women die young. That means my wife will live a long time.

Literal

Beautiful-woman short-life [quotative-とは] say [but-けれど]. Meaning, inside wife [topic-は] long-life [copula-だな].

美人薄命とはいうけれど quotes the proverb 'beautiful women die young.' The punchline — 'my wife will live long' — is self-deprecating humor implying his wife isn't beautiful. うちのかみさん is colloquial for 'my wife.' A great example of Japanese self-deprecating humor.