Babysitting

We have an event to go to next month my sister has 3 month old twins and we have a 1 year old. We have hired 2 sitting to watch all three babies together. What would you pay? This is the first time we are paying sitters so I really don’t know how much to give each girl. They are both 18-19 years old. Keeping in mind one is my SIL and her friend.