Are you asking about a brother donating to his brother and his wife (the sister in law), and how close the DNA would be? Because they are brothers and have the same parents there will be some closeness in DNA - but remember it will only be half, the rest will be the SIL.
Yes Gargy thats what I was asking - wanted reassurance that if they ever needed my DH's sperm that it would be "just like" using his.

Thanks again