I have always had an extra large one in the basement that the two cats have shared for years - the kitten had her own in the cage I was keeping her in because she had a parasite issue and had to be caged for the duration of her meds.
I really believe that she pee'd in the house because she is mad that I brought in the kitten - I don't think it is a litter box issue - she is just a brat.
I think we are going to rehome the kitten - we've only had her for three weeks so it will be easier to rehome her. I've had the other two cats for 11 years - can't make them leave - LOL!!!!
Hopefully once the kitten is gone - the other cats will straighten up.