Riddle

Two grandmothers, with their two granddaughters;
Two husbands, with their two wives;
Two fathers, with their two daughters;
Two mothers, with their two sons;
Two maidens, with their two mothers;
Two sisters, with their two brothers;
Yet only six in all lie buried here;
All born legitimate, from incest clear

The Answer to the Riddle

Two widows each had a son, and each widow married the son of the other and then each had a daughter