Couple of assumptions
- the population of the Chaoyang District (our district in Beijing) is 2289796 (2000 census)
- Most families don’t move to the other side of the world from each other so it’s not unreasonable to assume that you would have many generations of the same family living close by (and you said they both lived near by so I didn’t bother with the population of just your district)
- So let say a woman has two children, one boy and one girl (the one child policy is pretty new so this is totally reasonable). Each of them has two children, one boy and one girl. When the granddaughters are of working age you would have 4 women in the family who might be in the field (since you said the second girl was a niece I had to assume her mother or father had a sister or I would have only counted 3)
- Not that odd for a career to follow a family so it wouldn’t be odd that they all were in the same vocation.
So that’s 4 out of 2,289,769 or 1 out of 572,499... given the best set of circumstances that sounds right.
As a follow up: it turns out that the niece was not interested in part time work, so we will not be employing multiple members of the same family.