He is very adorable! I love the dark sables too. Yes, it is very common for males to be bigger than the females. They can bite/play bite each other and it is totally normal as long as there is no flying poop, blood or screaming (by the ferrets, not you lol). It sounds like they have adjusted to each other very quickly.
We took the bun feet off our couch too, but they quickly learned they could still get in the back of the couch through the cushion side *roll eyes* The only ferret proof couch is a futon, for the most part. Congrats on your new additions!