Whyever would you need to have 3 litter boxes? I could possibly see 2 since you'll have three cats, especially if your witchy-poo doesn't accept her now housemates. I have three cats, all females. We have one 1/2 litter boxes (a full size one in the bathroom and a small one in the utility room in case the bathroom door is closed). There are no spats over them, and one of mine is slightly antisocial too. I scoop solid waste every day, and totally replace the litter once a week. I don't use clumping stuff because the type I use is flushable. My litter lasts forever, I usually only buy one bag a month and it's not huge.
They also share feed/water dishes. We have a dispenser for both so there's only one water dish to rinse out and fill every morning and I usually fill the food dispenser 2x a week. I don't have a problem with them over eating (I did at first when I introduced it, but then it leveled off and they're at a good weight now, according to their vet). When we give them canned food, their portions are in separate dishes and those dishes are spaced out across the kitchen floor. Except for my Toni. My youngest daughter likes feeding her at the table. LOL The darn fur ball sits on my daughters high chair which is the perfect height for her to eat out of her dish that's sitting on the table. It's really cute.
Also, during the summer, all of the fur balls come and go as they wish through their little door.
And if your husband initiated this, he should totally help clean up after them! Your 4 yo can also help take care of them. My 4 yo loves her cat duties and doesn't even balk at taking care of the cat box. :)