Need help to find story about 2 sisters together

The story was a multipart story that had 2 sisters explore their sexuality together. I remember that the POV sister watched her sister have sex while hiding in the closet. The POV sister also wanted to try to use her brother to learn about hetero sex. I remember the sisters working a job in a coffee drive through and they would get tips from customers for flashing and it escalated to a HJ at some point. Some of the details might be merged from another story