PUZZLE: Family Connections

Here's one from Lewis Carroll's A Tangled Tale. (This one is easier to solve if you use a chart like a family tree.)

The Governor of Kgovjni wants to give a very small dinner party, and invites his father's brother-in-law, his brother's father-in-law, his father-in-law's brother, and his brother-in-law's father. Find the smallest possible number of guests.