Hi Danibooer,
I understand you do not wish to have Automatic Downloads on your iPad Mini and iPhone 6, but sometimes this option is enabled. The resource below explains how to turn the feature on, but you would obviously do the opposite steps to turn the feature off. Check to make sure you have the option turned off in your cellular data settings as well. For testing purposes, I would also suggest you turn the feature off on your computer.
Turn on Automatic Downloads - Apple Support
https://support.apple.com/en-us/HT202180
You can turn Automatic Downloads on or off over your cellular network on an iPhone or iPad Wi-Fi + Cellular. Go to Settings > iTunes & App Store and turn Use Cellular Data on or off.
If your iPhone, iPad, or iPod touch has an Internet connection and you turn on Push Notifications, your content automatically downloads to your device. On an associated device that doesn't support Push Notifications, your content automatically appears in your iTunes download queue.
One more thing you can try is to check the settings in the iTunes application on your computer.
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In iTunes, choose iTunes > Preferences.
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Click Devices.
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Select “Prevent iPods, iPhones, and iPads from syncing automatically.”
If this checkbox is selected, any connected iPod, iPhone, or iPad won’t sync automatically, even if “Automatically sync” is selected in the Summary pane.
If the issue still persists, you may need to restore the settings on your iPad mini and iPhone. The instructions below for the iPhone are the same for your iPad mini.
Reset iPhone settings - iPhone
http://help.apple.com/iphone/8/#/iph7a2a9399b
Reset iPhone settings. Go to Settings > General > Reset, then choose an option:
Reset All Settings: All your preferences and settings are reset.
iPad User Guide - Reset All Settings
https://manuals.info.apple.com/MANUALS/1000/MA1595/en_US/ipad_user_guide.pdf
Reset iPad settings
Reset iPad settings. Go to Settings > General > Reset, then choose an option:
Reset All Settings: All your preferences and settings are reset.
Take care,