So, why don't you give us some details...such as:
Are these male or female cats?
How old are they?
Are they spayed/neutered?
Are they always indoors, or indoor/outdoor?
If indoor cats, have they always been indoors?
Has this been a problem all along, or is this a new problem?
Are there cats outside who hang around your house?
Have you changed food or litter brand/type recently?
Where are they going, exactly? Near the box, behind things, in a shoe, etc.
We're glad to see you here, and hope that we can help!
Love All Life, Thank You For Posting! :)