Luckily my DP didn't take much convincing at all, especially as he stays home with the kids whilst I work full time so he does most of the nappy changes.
I just explained all the benefits to him, cost was a big one that he liked plus not having all those chemicals next to their skin. He loves cloth now and wouldn't put a disposible on DD even if he had the choice, his mum bought a pack of disposibles to keep round her house for when we visit or if she's watching them for a couple of hours for us and DP told her quite firmly that if she put a disposible on DD he would not be happy
He's also got quite knowledgable about them now, knows the difference between fitteds and pockets and AIO's, is a dab hand with a nippa(in fact he's better than me
)and loves telling people how fab cloth nappies are.
I agree with the previous poster, with twins the cost for disposibles will be huge so I'd keep telling him how much you'll save by using cloth, good luck with convincing him