A man with a beautiful wife needs more than two eyes.
Literal
Beautiful-person [possessive-の] wife [object-を] had person [topic-は] eyes [subject-が] two [by-では] not-enough.
美人の妻を持った者は is a relative clause. 目が二つでは足りない means 'two eyes are not enough' — he needs to keep a constant watch. A humorous proverb about jealousy. では marks 'with only two' as insufficient.