Bluetooth

You cannot pair an iOS device with another computing device, be it a Mac, PC or iPad, except for sharing an iPhone’s cellular connection. What are you trying to accomplish by pairing? Most functions that you might use pairing for can be accomplished using AirDrop or Continuity. See these support links:

Use AirDrop on your Mac - Apple Support

How to use AirDrop on your iPhone, iPad, or iPod touch - Apple Support

Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

You don't, sorry. No way to connect via BT an iPhone to an iPad and viceversa.

Regards

Giulio