Kittens, worms and their living space

We have 3 kittens living in an isolated room of our house. We treated them for worms when we first got them but they either somehow contracted roundworm again or never got rid of it in the first place. We are about to start treating them again but I was wondering if we should throw out their toys and furniture? We have cat tree type furniture in the room and it's pretty expensive so I didn't want to throw it away but I don't want to keep it around either if worms or larvae could be living on it and infect them again.

No need to toss the toys.  It often takes multiple treatments to completely rid the body of the parasites due to the life cycle of the parasites.