Gonna start babysitting. Any advice ?

So I’m a SAHM to a 16 month old baby girl I’m 19 years old and when I was pregnant so was my MIL so I have a 17 month old brother in law who I watch along with my daughter everyday. Now I watch them both completely by my lonesome on Tuesdays and Fridays. I watch them by my lonesome from 2pm to 4pm on Mondays, Wednesdays and Thursdays because on those days my FIL is home in the mornings and he helps by changing his son and putting him down for naps etc all I do while he is here is feed him breakfast and lunch along with my daughter which isn’t hard but still he is very attached to me so he’s usually spending time around me anyways Imm gonna get to the point. My boyfriends family has a friend who has 2 daughters, his youngest is 2yo almost 3. When she was a year and 6 months old they sent her out of the country to live with her grandmother in El Salvador because they had nobody here to take care of her for them while they work and go to school. She was out there for 6 months and it broke my heart. Anyways she’s back and they’re struggling again with child care and I’m going to be honest I’m a complete stranger to this family the husband has met me or seen me like 3 times while the wife has only seen me once and they called my boyfriend two days ago asking him oh so desperately if I could watch their daughter for them. My boyfriend said he would ask me and he would call them back. When he didn’t call them back they started calling him again so I answered and they told me if I could please watch their daughter for them from Mondays-Thursdays from 730am to 2pm they would drop her off at my home and pick her up and they would bring her to me with all her toys and meals already prepped. They said she’s very calm and no trouble at all as they know that I already watch my daughter and baby brother in law. This family will be coming over to my house on Saturday to discuss me babysitting for them and whether I will do it or not. I feel really bad for them and I would like to help them they even told my boyfriend they would pay me. Now my question is this can anyone give me some advice ? In all my life I have never taken care of children by myself besides my younger brothers and now my daughter and BIL I need advice on will it be hard ? What should I ask the parents when I see them this weekend ? I know to ask if their daughter has any allergies I should know of or medications she’s supposed to take ? But what else should I ask and I also don’t know what I will say regarding payment I don’t like to seem greedy or interested just for money but I also don’t want them to try to pay me to little so I don’t know what to do just please any advice would be great on how to care for a new child ! Btw she’s also potty trained so that’s a plus !