Help!

Jenny
We've had two sister cats that were left behind by a roommate 12 years ago. She brought them home one day because our unit allowed pets and moved out six months later. We became cat people and have spayed them, paid for countless vet visits and surgeries, and have loved them as our own. They've had issues with peeing outside of the litter box and we know nothing can be left on the floor, rugs and mats are out of the question, so on and so forth. We've had bloodwork done on both to ensure nothing was wrong, changed their food to expensive Science Diet c:d stress as recommended by the vet and they still randomly pee just outside of the box. The box needs a cover or they stand in the box and pee on the floor. They are not arthritic. Both of them do this. I'm 8 months pregnant with number 2 and we have a 2 year old who is very gentle with them. I'm at wits end and I don't know what to do anymore 😭
We scoop daily and clean floors around the boxes daily.