I have 2 boys aged 1 and 4. Potential nanny has a 2 year old daughter that she would bring. Does anyone have experience with this?

This is what i have come up with:
Pros:
- cheaper rate
- play mate for my 1 year old when 4 year old is in school
- slightly older play mate for my 4 year old when he is home

Cons
- less focus on my kids
- less time to do extra stuff around the house (i don't ask a whole lot, but typically it is a nice bonus of having a nanny that everything is cleaned and i can leave laundry to fold etc)

anything else?