Firstly....are all your cats neutered? And when did you move? Cats toilet to mark territory as well as to "do their business." So if they're toileting where they shouldn't, that may be the case.
Also, if you have four cats who you are keeping as indoor cats, you may need to look at the amount of litter trays you have available to them. Remember they're used to not HAVING to use the same area to toilet.
Mimicking the mental stimulation they'd receive from outside matters too. Interactive toys, large posts with cubbies and shelves are all quite important to ensure they feel they've enough freedom to be themselves.
Scent marking areas they can scratch with catnip spray and can't with something like Pet Behave Spray can help too.
If it's possible, cat proofing your garden may help matters as well.