However, here are some possibilities you could use:
Formal:
* A staff of maids
* A retinue of maids
* A company of maids
Informal:
* A group of maids
* A team of maids
* A crew of maids
You could also use a descriptive phrase like "a bustling crew of maids" or "a hardworking team of housemaids".
Ultimately, the best collective noun will depend on the context of your writing.