Recommendation Letter Ethics

This is so strange, but my mother married my 9th grade AP Physics teacher in my 11th grade year. I’m applying to college as an astrophysics major, and planned to have my AP Physics teacher write my letter of recommendation. Is that still an okay thing to do? My passion is physics, and this is the course I shine in most distinctly. Am I morally obligated to approach another teacher for a recc letter? Thanks.

I would ask another teacher not only because 1) it is sticky ethically asking your step-father for a recommendation but more importantly 2) because it is best to ask a teacher from 11th grade (possibly 10th) for your recommendation – hopefully you have grown and evolved as a student between 9th and 11th grade and you want your recommendation to reflect that growth. I’ve never heard of any student asking a 9th grade teacher for a LOR.