how to get rid of giardia in the house?

we are on month 8 of parasites and i’m so so tired. very very long story but basically we adopted bonded 6 month old kitten sisters in january who came home w coccidia and giardia, and they didnt even test positive for giardia until july. their first round of giardia treatment (14 days of metronidazole) failed as after a couple weeks they became symptomatic again. and i guess we can’t even be certain the coccidia is gone, although id like to think it is based on the difference in symptoms. they have access to the whole house (they were in quarantine for their first two months home until the vet gave us the all clear to let them out… but they were still sick). we did above and beyond the vet’s advice. also their litter boxes and water fountain are stainless steel and their food bowls are ceramic

what are your experiences getting rid of it in the house once they get on their next dosage of meds?

our money situation is extremely tight, especially after the thousands of dollars we didn’t have to spare of vet bills and previous prescription food and replacing of stuff etc. thinking of throwing away all their things makes me want to cry, is that really important? i’ve heard such mixed things. we have one rug and all hard floors otherwise, but they do sit on fabric furniture like the upholstered kitchen chairs and living room chair. i’m very chronically ill with limited mobility and my partner works a very physical job full time, we have very little mental and physical energy left after dealing with this for so long now. no fear mongering please, but also be honest about what we need to do to get rid of it. i’m so so sad for my poor babies, they don’t deserve this