Please take them to the vet and tell the vet what they are doing. Peeing outside the litter box is the #1 symptom of urinary tract problems!
If the vet says they are okay, then consider making a few changes.
If you use a covered litter box, take off the lid. Many cats refuse to use covered boxes.
Cats prefer fine grained unscented litter. So, you might try changing litter.
Make sure you have at least one litter box per cat.
Make sure you scoop the litter box daily, and with multiple cats, scoop twice daily. Cats often refuse to use dirty boxes.
If your litter boxes are real old, they may have absorbed odors even if you regularly clean them. So, try buying new boxes.
Make sure your litter boxes are in a place where the cat feels safe while going potty. If she is disturbed by you or your kids(?) or the other cat while she is trying to potty, she will choose to use a safer location. So, move the litter box to a location where she can see the comings and goings of the other people & animals in the house.
Put a litter box on each level (floor) of the house.
Make sure you thoroughly clean all old urine spots on the rug and elsewhere. If they can smell the old urine they will think that place is a good place to pee. Use a flourescent black light to find old urine and treat all old spots with an enzymatic cleanser.
Try putting a plastic carpet runner upside down on the places they like to pee....most cats don't like to walk on the "spikes" so they will avoid the covered spots.
Keep the bath mats on the edge of the tub instead of on the floor. Also, try bath mats and rugs that do not have the rubber back. There is something about the smell of rubber that induces some cats to pee on throw rugs.
Sprinkle the rugs with a really smelly carpet fresh powder. Leave the powder on for several days so it will "stink" too much for the cats to use the rugs. Refresh the smell about once a month (or more often).