It’s def possible but it always looks better when you see it to fit exactly. Or reupholster the cushions
No, sheets are too thin a fabric to use in such a way. I mean for a short time or as dust covers they would be fine. But not to sit on. I used very thin fabric on this sofa, but I quilted the fabric before cutting it for the sofa cover pieces. Corduroy would be o.k., or denim, Or you could use a couple of cheap coverlets. I have grown to always prefer leather or even a fake leather as it is washable and very serviceable.
Absolutely! I have a good friend with a cat that uses her sheets for covers and removes it when guests come over. If you want to make them more permanent, add elastic to the edges. They work very well and are washable!
I guess it depends - I tried using a sheet to cover a couch in college - and the sheet would always come off and it was annoying. We bought an ugly cheap couch to cover in our cheap college apartment. But if it is something just to cover where pets are, then go for it! Otherwise I'd spend the money on a real sofa cover.
Food covers using starched doilies