Look at the family tree again.Who is/are:
1 twins?
2 Bill`s parents?
3 Bill`s grandparents?
4 Mike`s son?
5 Sam`s wife?
6 Janet`s husband?
7 Sue`s daughters?
8 in their late sixties?
9 in his mid forties?
И пожалуйста скажите,как узнать,где ставить are,а где ставить is и приведите пример и пожалуйста скажите правило.

1.   twins? — Kim and Kate

2.   Bill's parents? — Sue and Sam

3.   Bill's grandparents? — Tom and Beth

4.   Mike's son? — Johnny

5.   Sam's wife? — Sue

6.   Janet's husband? — Mike

7.   Sue's daughters? — Kim and Kate

8.   in their late thirties? — Mike

9.   in his mid forties? — Sam

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1) единственное число или неисчисляемое существительное - is. 

2) множественное число - are. 

3) I - am, 

    he/she/it - is, 

    you, we - are. 

There is a chair near my bed.

There are two chairs near my bed.

3. He is my best friend Nick.

4. You are my best friend.