Welcome to our Community! I can tell that you have already done some research on your family tree. It's great that you plan to see where your ancestors came from.
The first tip I can give you would be to search the County Mayo
genealogy centers through Roots Ireland for any surviving church records (a birth/baptism certificate of James for instance). You can also contact them to see what they can do to assist once you arrive in August.
Maybe some of our expert genealogists will jump in!
Best of luck and let us know how your search goes! We are also here to help should you need tips to explore the north west of Ireland.