D..
What I don't know from what I'm reading here is if you are paying a set amount or by the hour. You also haven't told us if you are unhappy with the cleaning.
If you are paying MORE because it is taking longer to clean, or because she is expecting the son to be paid, that's one thing. I have to admit that I am surprised the boy cleans - most 14 year olds would just laze around and play a gameboy or read or watch TV. This young man actually knows what it means to not be able to "have" - perhaps he understands what it means to not be able to pay the bills.
If you were starting out new, didn't have the experience of having had the other woman, and accepted the time frame of late afternoon into the evening, then I doubt this would bother you as much. I would think that the woman is training her son to be able to get a cleaning job with a company, by starting him out cleaning in a home.
What is his attitude? Is he a smart aleck? Does she pay attention to the details of his work? If he misses something, does she fix it or have him do it over?
If you are happy with the cleaning and if the son is not rude, if they are both honest, and if you are paying by the job and not the hour, I hope you will put your irritation aside and keep them on. You could have them start downstairs or in the common rooms when they arrive, and closer to dinner, bathrooms and bedrooms so they won't be underfoot so much.
Once or twice a month isn't bad, really.
Dawn