Idioms

Like chalk and cheese

Sample:

Q: Do you have any siblings?
A: Yes, I have an older brother, he is married and works as an accountant in an advertising company. We are like chalk and cheese, he is active, confident and outgoing while I am the opposite.

Like two peas in a pod

Sample

Q: Who are you closest to in your family?
A:

Down to earth

Off the top of my head

On the fence