I’m sure you can’t be the one to tell your mom (parent/child deal), but for your knowledge, there’s nothing at all about a Christian college that stops one from opting to change their life from how they were raised. I work at a public high school and know plenty of students who choose Christian colleges along with my own son’s experience. Every single one of them has told me kids will do what they want to once away from home. They just might have to hide more if the rules are strict.
What you or your brother or anyone does once they are in their upper teens to adults is totally up to them. It’s the way our brains are designed. Your faith is either yours or it isn’t. There are actually a fair number of students from non-religious homes that come to faith once out on their own too.
Getting back to considering school searches, you’ll need to look for those offering considerable merit aid and that’s easier to do once you have your official scores from March’s test. Until then google Christian colleges, see what pops up, and do some “college hunting” to see if any look appealing keeping merit aid in mind. Union (TN) is still one to consider IMO. I fully understand some parents insist on Christian Colleges. It happens. Your life and med school life won’t be doomed by attending one, so find some options you like that are potentially affordable. Grove City is one local students like that is often less expensive than others, but I don’t know if they have large merit awards. You can check if they look appealing. Taylor gets good comments, but again, I don’t know their merit awards. My own lad enjoyed Covenant and they were affordable for us at the time (he graduated 5 years ago).
I’m thinking you could also look at some secular schools to have as comparisons. If you show your mom the Christian clubs available at these places she might realize there are intelligent and faithful Christian students in pretty much every college. This could come in handy if they end up being more affordable.