Is it possible that a female cat wont use the litter box after the male?

I hope someone can help, i have two males and two females, and the two females will not use the litterbox, they used to untill the males arrived in the house..and i dont want to get rid of any of them, they are my babies and i cant do it..but theres got to be a solution, they are all healthy cats, see the vet regularlly, no infections..i just dont understand, im having my carpets cleaned proffesionally in the next month and maybe that will help, but my b/f seems to think its because we have males..oh and all of my cats ate fixed..please help if u can..thanks

Have you tried seperate litter boxes? Try putting one or two more in seperate areas of the house.

Some cats won't use the same litterbox as another cat, it's to do with dominance and territory - in a multicat household it's apparently best to have 1 box per cat and 1 spare, if you have room for it - but at least have 1 each.

My females avoid the boxes the male pee in. Poop, they don't care, but they avoid the pee ones.