Hi
Apple's information regarding display pixel anomalies is provided here:
About LCD display pixel anomalies for Apple products released in 2010 and later - Apple Support
I suggest that you contact Apple Support (mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider including, if recommended, to arrange for each iPhone to be inspected and to establish any available service options (whether under warranty, if eligible, or via chargeable repair service):
iPhone Service Answer Center - Apple Support
I'm afraid that no-one here can tell you what Apple will decide. You are not talking to Apple here - this is a user-based technical support community.