Hi there and welcome!
i like your kitty names! They are adorable! Very intelligent-sounding.
i guess i am making different speculative guesses here.. and one is that your baby Charlie might not like the current TYPE of litter. i tried many types of litter, and did quite abit of research before settling with theworld'sbestcat litter. This litter is great and is odorless. It is made of whole corn kernel.
i read somewhere it is best to place the kitty litter box at a convenient location... not "miles" away, as it would be a "chore" just to gain access to the toilet. Would you consider placing the litter boxes at a more convenient or preferred spot? Oh, it is recommended not to place the litter box too close to where they eat.
Also, i read that one litter box PER kitty. So, you should have two litter boxes?
i think it is also vital to scoop their undesirables several times a day. Just like us, they don't want to use a dirty toilet. Oh btw, i think metal scoops are better as they will not absorb odor.
i wash my kitty litter box scrupulously clean once a week with detergent and extremely hot water. After i blow dry the boxes, i replenished with new their litter. i think it is really vital to keep the toilet area very clean (i use a hand vacuum to do pick up jobs.)
Don't know how much i have helped.. but hope your problem is resolved pretty soon!
Take care of you and take care of Charlie and Chester!