How do I tell the owners of two senior dogs that I've been sitting for a year that I no longer want to sit for them ?

I've been dog sitting these two senior dogs for a year. One dog is very relaxed and easy going the other has countless issues due to his age (14). Both dogs require medication every day. The 14 yr old dog takes about 8 pills every day and has been constantly peeing all over my house and keeps waking up at night and whining like a howling deep breathing whine .In fact he whines about 80 % of the time. The whole weekend I wasn't able to sleep because he kept waking up and whining. I feel like he is use to getting up at 5:30am and eating because even if I let him out he would continue to whine. The other senior dog, is a little bit younger but has developed pickiness toward her food lately which she wasn't been before and would not eat her pills even with the use of pill pockets (which I had to go out and purchase). I've also tried the sticking it down the throat approach but they always manage to spit them out.

I felt like taking care of them a year ago was much easier than it is today and that I should breakup with their owners and request they find a new sitter because we aren't a good match anymore. Ive been asked to watch them again in two months and feel like I cant go through a week of constantly cleaning pee and loosing sleep and spending thirty minutes trying to get them to eat their pills when I have to work 40 hours during the week. Also on top of all of that I dog-sit both dogs for only $25 a night. This is the rate they requested in the beginning and it had been set when I first started out, so I was willing to do it at this rate but now I realize these dogs are too much work and too high maintenance for me to continue putting in so much work. What would be a nice way to break up with the dog owners? They are so nice but Idk how to tell them I just can't sit for them anymore.

Also should I tell them in person or over text that I cant dog sit for them anymore?