I think you should use Hosannah as the fn, especially if you plan to call her by it. Learn from my mistake. We named our son Edward Liam. Won't go into the story behind the names, but we call him Liam. Everyone calls him Liam. 1st day of school, his preK teacher insists on calling him Edward. My son won't respond to that name. I fought with this very stubborn teacher every day. She wouldn't budge. It got ugly. Had to transfer him to another room. We're in the process of legally changing his name now.
Also went thru this myself growing up. My name is Alma Corina. Family calls me Corina. Was called Alma in school. To this day people call me by both names. I have family members that have no idea my first name is Alma.