I, personally, don't see that there would be a problem with adopting Sven. His being declawed shouldn't be an issue with your other cats. When you bring him home, there will be an adjustment period as he settles in, but usually cats don't get past the hissing and growling stage as they define their "pecking" order -- so they shouldn't be fighting with their claws. And, since he's going to be an indoor cat, he won't have to defend himself outside.
He sounds like a beautiful cat. You posted a while back and didn't get any replies; so I hope you went ahead and made him part of your family.