One thing that would make it easier would be to go to Window>Model Info>Components and tick both of the Hide boxes there. That’ll let you hide the rest of the model while you are editing a single component or group. I looked at one of the stuffed chair components. The bottom shows a lot of edges and faces that aren’t needed. Once you erase the bottom of the base, you can get access to the bottom of the chair itself.
You could remove the faces making up the underside of the seat cushion for example as well as some other internal geometry.
You could delete a lot of the undercarriage of the couches, too. It looks like the author put in some of the detail required to make them.
Unfortunately I haven’t got time today to go through all of your model and fix it. I’ve got work I need to get done for a client.