cats not using litter box. how do i fix this?

i have 4 cats. 3 of them are a year old and the other is a kitten. the kitten uses the litter box but for some reason my older cats have not been wanting to use it. they go all over the house and it is really starting to get annoying, this has been going on for about 2 months  . i keep there litter box clean and i use the same litter as i have since they were kittens, the litter i use is a all natural litter and it works great for the smell. how do i fix this problem? 

How many boxes do you have? A good rule is one box her cat, plus one extra. If they're all going in the same box, they could be showing behavioural or territorial signs that are intimidating for other cats, forcing them to find another place to eliminate. Also, if you don't scoop after every single elimination (tough to begin with, let alone with multiple cats), they just may not want to use a dirty box. It's like trying to use your bathroom before your housemate(s) has/have flushed.

If it doesn't seem behavioural and you have enough boxes, it may be worth checking in with a vet - could be something offputting in the kitten's waste, or the adults may not be feeling well. Unfortunately there can be many reasons for inappropriate litter habits.

well i think the main problem is that i don't have enough litter boxes . i will have to get some more and see if that helps. thank you 

If this is the case, it may be a very quick fix for you! If you just get a few other litter pans, even some smaller ones, at least they'll have the option of relatively clean litter all the time. Good luck!

Once you get more boxes, don't put them all in one place though, that's no different from having one box. Each box should be easily accessible. You want each cat to be able to use a box without any of the other cats "bullying" one (blocking access for example). If you can, make sure the boxes each have 2 escape routes, and put them in a somewhat hidden area for privacy.

Make sure the boxes are big enough for them to stand in and turn around -- rule of thumb is at least 1.5x the length of the cat. Uncovered is usually best.