My partner and I rehomed 2 kittens just over 5 years ago.
So after visiting the shelter and deciding to give these 2 kittens a home (they are siblings), the rescue lady brings them to our house and causally drops into the conversation that one of them throws up a lot. She isn’t sure which one and to feed them the cheapest blandest food from the supermarket 
So I researched and tried various things things to stop him being sick; feeding grain free good quality food, feeding them in separate rooms, various strategies to slow down his eating etc.
Over the years some things seemed to have improved the problem for a bit and then for seemingly no rhyme or reason he’d be throwing up again.
So as well as the boy throwing up the girl also like to eat grass and be sick and cough/puke up hair balls frequently.
They both have had numerous vet trips for viruses and tummy upsets. The girl has never learnt to retract her claws properly so most clothes/furniture/fabric that she has been on get threads pulled and ruined.
We’ve dealt with shit and piss on brand new sofas and in the bed.
And now tonight I found a flea on my daughter. Yes, sometimes pets get fleas and we regularly treat them but something in me just snapped and I feel like I’m on my last nerve with them. We’ve tried so hard with them and I don’t know what I can do to resolve the issues I have. The being sick, the claw thing. I know I’m a horrible person for thinking of rehoming but its been brewing up in me for a while and I need to find a way to live with these cats without resenting them.
Any advice??