Remember, the home button routes through the screen so a faulty screen can throw up some weird home button errors. Definitely try another screen if you haven't already.
Whenever a new iPhone is released, there are sub-par small parts on the market for a while. Your front cam flex might be one of the lemons. If they all don't work, maybe try replacing the physical speaker.
Absolute worse-case scenario - If you have actually damaged the home button, you could always do your best to restore it to the original parts and tell the customer to go to the Apple store. If Apple agree to do an out-of-warranty replacement, it can work out cheaper than a new device from a retailer. You can refund the customer for the repair + extra for the Apple replacement. Hopefully you don't have to explore that option though! Best of luck mate