I'm assuming this is some trick thing like "2 sons and 2 fathers are 3 people because you gots a son, a father and grandfather, the son and father are the sons and the father and grandfater are the fathers"
might be easier to draw as a tree
so
grandfather, grandmother, 2 fathers (1 is a grandfather), 2 mothers (1 is a grandmother, 4 children, 3 grandchildren (these are 3 out of 4 children), 1 brother (1 of the children), 2 sisters (2 of the 4 children), 2 daughters (these are the 2 sisters), 1 father in law, 1 mother in law, one daughter in law (one of the sisters)
see diagram/attachment because it is confusing
in the diagram, m=male and f=female
ok, to expain
let's give them names
the grandparens are bob and mary
their kids are jim and jill
the kids of jim and jill are adrian, sally, and kim
bob is the grandfather
mary is the grandmother
the 2 fathers are bob (father of jim) and jim (father of the 3 kids)
the 2 mothers are mary (mother of jim) and jill (mother of the 3 kids)
the 4 children are the 3 kids of jim and jill and jim (child of bob and mary)
the 3 grandchildren are adrian, sally, and kim
the brother is adrian (brother to sally and kim)
the 2 sisters are sally and kim (sisters to adrian)
the 2 sons are jim (son of bob and mary) and adrian (son of jim and jill)
the 2 daughters are sally and kim (jill is also a daughter but whatev)
the father-in-law is bob who is the father-in-law of jill
the mother-in-law is mary who is the mother-in-law of jill
the daughter-in-law is jill who is the husband of jim who is the son of bob and mary
7 people total
so then we do 2*7=14
14 burgurs
assuming you are bob or mary or one of the people in attendance
