what would you do

My bfs parents own a restaurant and I worked there 3 years ago that's how I meant him. I quit and we broke up since I was 16 at the time. Well a year later we got back together and have been together since. I have just moved out of state with my family and am going to visit my bf next weekend. I have to fly to him and they are letting me stay with them/feeding me ect, they are very nice and want me to feel welcome. Well they need my bf to work next Friday and said I could too. Here's the thing I wouldn't go to make money I would go to help them since the are short staffed. I feel weird having them pay me especially since they are paying for food and anything else I need at their house. What would you do? I feel like I'm family so they shouldn't pay me for one night. I feel weird if I take the money. It would be about $50-70 probably in cash. My bf thinks I'm crazy but I feel weird having them pay me. Especially since I forgot some things, don't know everything, and can easily screw up. I don't want them to feel obligated to pay me but I know they will insist. How do I handle this? If I had to stay in a hotel, rent a car and buy food it would be. 500+. Should I just tell them I will help since they welcomed me over and all?