Derwitt Duddly had an assignment to draw a picture of his family.
“They won't all fit on this piece of paper,” he wailed loudly in class.
“What exactly is your problem, young man?” inquired his teacher,
Ms. Im. Patient. 

My family has 1 brother, 2 sisters, 2 sons, 2 daughters, 1 grandmother,
1 grandfather, 2 fathers, 2 mothers, 4 children, 3 grandchildren , 
1 father-in-law, 1 mother-in-law, and 1 daughter-in-law, and they won't 
all fit on the paper.

“I'm sure you can manage.” stated his teacher, emphatically. 

Can you help Derwitt out? What is the smallest possible number of 
people in his family?

The smallest possible number of people is 7. Tom and Maggie are married 
and John is their son.  John is married to Mary and they have two girls 
Sue and Joy, and a boy Bob.  Here is the family tree:

      Tom-----Maggie
           |
         John------Mary
             /|\  
           /  |  \
         /    |    \
      Sue    Joy    Bob


Let's check that out:

1 brother? Yes, Bob is the brother of Sue and Joy. There are no
           other brothers.

2 sisters? Yes, Sue and Joy are sisters to each other and to Bob.
           There are no other sisters.

2 sons?  Yes, John is Tom and Maggie's son, and Bob is John and 
         Mary's son. There are no other sons.

2 daughters? Yes, Sue and Joy are the two daughters of John and Mary.
             There are no other daughters. 

1 grandmother?  Yes, Maggie is the grandmother of Sue, Joy and Bob.
                There are no other grandmothers.

1 grandfather?  Yes, Tom is the grandfather of Sue, Joy and Bob.
                There are no other grandfathers.

2 fathers?  Yes, Tom is John's father and John is Sue's, Joy's and
            Bob's father.  There are no other fathers.
            
2 mothers?  Yes, Mary is Sue's, Joy's and Bob's mother and Maggie
            is John's mother.  There are no other mothers.
              
4 children? Yes, if you count a grown married man, John, as a 
            "child".  John is the "child" of Tom and Mary. And Sue, 
            Joy and Bob are John and Mary's children.  That's 4 
            children.  There are no other children.
            
3 grandchildren?  Yes, Sue, Joy, and Bob are the three grandchildren 
            of Tom and Maggie. There are no other grandchildren.
            
1 father-in-law?  Yes, Tom is Mary's father-in-law.  There is no
            other father-in-law.

1 mother-in-law?  Yes, Maggie is Mary's mother-in-law. There is no
            other mother-in-law.

1 daughter-in-law? Yes, Mary is Tom and Maggie's daughter-in-law.
            There os no other daughter-in-law.  

Edwin