2 cats, 1 diabetic, other pees outside litterbox

I have 2 cats that are 7 years old. Over the last 5-6 weeks there has been frequent peeing on bedding, and area carpets. We took them to the vet and only one provided a urine sample. He turned out to have diabetes. They were also both put on Amoxicilin for possible UTI. The accidents have kept occuring and we narrowed it down to the cat without diabetes. We only have 1 litterbox (I know...), and are trying to figure out a multi-box set up that works with having a 7 month old that get into EVERYTHING and puts everything in his mouth. Any insight would be appreciated.

They also drink a lot more water than they used to and it does not have as strong of a cat smell.

I would recommend getting the other cat tested for diabetes as well. More frequent drinking and urination and peeing out of the box are all indicators of a medical issue. How are you going to treat for diabetes? While insulin may be warranted, a high animal protein, low carb diet has helped cats with diabetes.

As for litter box set up, not sure what to recommend that your toddler can't get to unless you can place a litterbox high enough that he can't reach.