What's a good age to babysit three kids?

My sister and I are twins and got asked if we could babysit our neighbors three kids next year. My sister and I have no experience with babysitting as not many people in our neighborhood have little kids. We are going to be 15 and we are going into 10th grade. There are two girls and one boy. The oldest girl is going into third grade and the other sister is going into kindergarten. The little boy is two years old. Do you think were capable and old enough to handle the three kids? What do you think is a good age? We would be watching them twice a week (weekdays) from 3-5pm. My sister and I know the obvious like watching them at all times, especially the little one and not letting them go crazy or get into things.