Please Help! My cats keeps spraying everywhere!

So I have 4 cats, I know it’s a lot and I will never have more than two again in my life. We have two boys and two girls and they all get along other than them picking on each other they all sleep together and can eat near one another without any fighting and they don’t steal food either. It all started about 4 years ago when we moved for the first time with our oldest girl cat started spraying the walls. At first it was just her but then one of our boy cats started doing it and then our youngest girl started peeing on the floor by the walls and then learned to do it on the walls as well. We’ve changed their litter, we have 5 boxes and we’ve been cleaning the spots with an enzyme cleaner but nothing has stopped them. I took the first girl cat to the vet and explained everything to her and she said she thinks it’s behavioral and that we should try to get the wall plug ins but I don’t want to spend tens to hundreds of dollars to put them around my house if they aren’t going mg to work and looking at the reviews it seems they won’t. I’ve been opening the back door and letting them go outside during the day so they cat spray out there if they want and get some different type of stimulation if they’re bored but they still spray. I am so tired of my house smelling like pee no matter how much I clean. I get so overwhelmed thinking about it I want to cry, get rid of everything and live in a hole. I have no idea what to do anymore. I’ve thought about putting them in separate rooms because the vet said that it might be because they don’t like each other. I’ve also thought about medicating our first girl because she’s kind of anxious and maybe that will help with the others because they learned the behavior from her. Rehoming them isn’t an option because we love them so much so please don’t say that. The vet also told us we could reach out to a behaviorist but that just sounds like a money pit. Also could them picking on each other mean they don’t get along and I don’t understand their relationships? Please help. Any advice is greatly appreciated. Also sorry for the run on sentences and incorrect grammar I’m too stressed to even worry about it I just want help.