What app would you recommend for this? Does it exist? Thank you
VPN doesn’t prevent gps tracking or tracking of what you are doing.
The solution would be to buy your own phone and plan instead of one your parents provided.
Look into developer tools 
might be able to use mock locations.
I doubt Apple would let an app circumvent the “Find My” feature with Apple devices.
You should probably just let your parents track you until you are mature enough to know how the world works without having to solicit help from strangers on the internet.
Let them keep you safe. Focus on making money so you can afford your independence and gain some wisdom.