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It sounds like 2 of your devices will not prompt to update to the new iOS over the air.
You can also upate the devices through iTunes if they will not update in Settings > General > Software Update
iOS: How to update your iPhone, iPad, or iPod touch
- Ensure that you're using the latest version of iTunes.
- Connect your device to your computer using the included USB cable.
- After iTunes opens, select your device when it appears in iTunes under Devices.
- Click "Check for Update" in the Summary pane to check for available updates.
- If an update is available, iTunes prompts you to download and install the update. Do not disconnect your device until the update has finished.
Note: To update your iOS device, iTunes needs to stay connected to the Internet. If your computer uses your iPhone's Personal Hotspot for its Internet connection, you'll need to update your device wirelessly or connect your computer to another network.