Which is correct?

They are of the same blood.
They share the same blood.




Both of those are good. I couldn't choose between them.

- They are blood relatives.

An interesting point is that you can have a dear relative, such as your sister's husband and you may feel close to them, but they are not of the same blood. In order for the sentence to be true, you must share a biological parent or grandparent (or another distant parent)

Hope this helps