Videos shot on an iPhone appear overexposed in iPads

Hello adam_bucky,

Given what you're describing, we'd recommend reviewing If a media file doesn't open or play on your Mac, iPhone, or iPad - Apple Support

When it comes to HEVC, per Using HEIF or HEVC media on Apple devices - Apple Support:

Support for HEIF and HEVC is built into iOS 11 and later and macOS High Sierra and later, letting you view, edit, or duplicate this media in a variety of apps, including Photos, iMovie, and QuickTime Player.

On some older devices, support for HEVC is affected by the resolution and frame rate (fps) of the video. Resolutions of 1080p or lower and frame rates of 60 fps or lower are more broadly compatible with older devices. To reduce the resolution and frame rate that your capture device uses for recording video, go to Settings > Camera > Record Video, as well as Settings > Camera > Record Slo-mo. 

If you're using iCloud Photos with iOS 10 or macOS Sierra, you might see a warning icon  in the upper-right corner of the photo or video, or you might see an alert message. To fully view, edit, or duplicate HEIF and HEVC media on your device, upgrade to iOS 11 or later or macOS High Sierra or later.

So this will depend on the iPad receiving the format and if it can properly view these kinds of files or if they might see some performance issues.

Take care!