There were two grandmothers and their two granddaughters....... legitimate and relationships clear. How can this happen?

Question

There were two grandmothers and their two granddaughters.
There were two husbands and their two wives.
There were two fathers and their two daughters.
There were two mothers and their two sons.
There were two maidens and their two mothers.
There were two sisters and their two brothers.
Yet there are only six, who are buried here,
All are born legitimate and relationships clear.
How can this happen?

Answer 1

If we have two divorced or widowed women marry only sons of each other we shall have...
Two mothers and their two sons
Two husbands and their two wives and

Now, if both couples had a daughter each then we get all the rest of legitimate relations...
Two fathers and their two daughters
Two maidens and their two mothers
Two grandmothers and their two granddaughters
Two sisters and their two (step) brothers