You have to marry your wife’s slightly hotter sister. That way you still only have one mother in law, but you double your chances for not getting any on a particular night.....
heh heh heh...
Slightly off topic; but I knew a fella, who had a sister.
He married a lady who had a brother.
The sister and brother got married to each other.
Genetically, the children of each marriage were more like brothers and sisters than cousins.
(Would that make his sister also his sister-in-law?)