I am glad that this story is different from the usual cliche romance novels, which I have started to seriously dislike so any thats different from the norm I check out. It has the romance, but its a gradual one both parties are likable so you can alway cheer for them, plus their age difference is not so huuge that it becomes distasteful (I hate over 10 year gaps; 2-8 is acceptable for me). Plus the FL seems reserved but intelligent. I am also glad its completed. As such I can enjoy its content in its entirety. This is a decent story. Congrats on your attempt.
Note that - you need the sisters need to be more aware of stranger danger even if its a first meeting. Our present society does not allow for immediate trust after a 1st hello it can be beyond costly.