Welcome to FT!
You might ask in the AF and NW forums if each carrier offers a family account.
I suspect that they do not and that you and your husband will each need you own number.
That said, you will have to decide which carrier to open accounts with and accrue miles to. As both AF and NW are SkyTeam, you should be able to open accounts with either and accrue miles with either, e.g., accrue miles flown on AF to a NW account.