Hi,
The iPhone and the iPad need to be using an Apple ID and to be on the same LAN
On the iPhone in Settings > Messages > Send and Receive you should add the Apple ID
The iPhone then needs to be on the same LAN as the iPad.
The iPad needs to be using the same Apple ID.
This will link the iMessages Part.
If the two are on the Same LAN then text Forwarding on the iPhone should be an option.
Also "Send and SMS" also needs to be enabled.
Enabling it should cause the iPad version to show a pop up with a Code Number on it that needs to be entered back on the iPhone.
8:25 pm Thursday; January 12, 2017
iMac 2.5Ghz i5 2011 (Sierra)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
iPhone 6 iOS 10.x and an iPad (2)