A reference to Rabbi Yehuda Gershon Pickholz in the book
"Meorei Galizia" says that he married the daughter of
Rabbi Meshullam Pickholz, who was therefore his brother,
his father-in-law and his brother-in-law.
I understand the father-in-law and brother - he married
his own niece. What other combination (not involving
second marriages) would make them brothers-in-law? Since
they were brothers, neither married the other's sister.
And since R. Yehuda Gershon married R. Meshullam's
daughter, they couldn't have married sisters. Or have
I overlooked something?