Why wont they use the litterbox

I have 5 cats. One female and two males and two male kittens 3 months. My female has had two litters of kittens, both litters have refuse to use the litterbox.. they will go beside the boxes but thats about it.. i have changed litter, gotten new boxes, move them around (had to move one back cause mom is blind and couldn't find it) but they will not use it. What do i do?