First, the sofa: The damage doesn't look impossible to repair, but I'd get it done fairly soon to prevent it from getting worse (even just people sitting on the furniture, etc.). You can probably find an upholsterer who will make a house call for the sofa arm, so you don't have to take the whole thing in. The cushion can be taken to the shop. Then, I'd cover up the furniture until they learn not to chew things that don't belong to them.
Which brings us to chewing the wrong stuff. Tallulah is 4-1/2 and still chews constantly. She chewed through a leather leash in two places during a 15 minute car ride. Now, I've learned to take her leash off and take a chew toy in the car. When she first came home several weeks ago she was allowed free in the house during the day when I wasn't home (I crate her now, more related to potty training though). She didn't eat any furniture (luckily), but I still have a bunch of cardboard boxes sitting around from my move last fall (err, yesā¦last fallā¦), and she chewed one up one day even though she had toys to chew.
The next second I saw her put her mouth even near that box (or any other), she got a a very stern "leave it" in my deepest, firmest voice and I held her gaze until she backed off. And I gave her something else to chew in that same moment. A couple times when I saw her going for the box, she didn't listen and I had to physically intervene to distract her, by nudging her or sliding my leg between her mouth and the box. I always made sure to offer her something to chew that was hers at the same time. It only took a couple of days and she hasn't even looked at one of those boxes in a few weeks. Now, if she can just train me to unpack them...
Anyway, I figure it's a lifetime commitment to distract her from chewing things she shouldn't. Or doing anything to or on the furniture besides sitting or sleeping nicely on it (and the sofa also has a washable blanket on it where she sits). In general, I treat her like a toddler and she's never out of my sight for more than a couple of minutes. If I can't see her, I wonder what trouble she might be trying to get into.