Actually, I can answer it myself. I just figured it out.
The total amout to create a committee with 4 men and 6 women = 10 people is C(10,5)
The forbitten committees have the 3 sisters. So 3 of the 5 places in the committee are occupied by the sisters and we choose only people for the last two places.
We have 7 people to choose from (10 - 3 sisters = 7), so it is C(7,2)
Then we just substract the forbitten committees from the total possible committees C(10,5) - C(7,2)