If you simply wish to start again with the iPad, no data will be lost from your iPhone.
On the iPad, prepare it for a new user by following this process:
What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
This procedure will completely reset the iPad without any impact upon your iPhone - and will leave the iPad ready to set-up as new with your wife's iPhone.
These support pages should get you started with setup of the iPad - and the methods of transferring data and settings from your wife's iPhone to the iPad. During the process, keep the iPad and iPhone in close proximity - and your own devices well away:
Set up your iPhone, iPad or iPod touch – Apple Support
Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support
Use Quick Start to transfer data to a new iPhone, iPad or iPod touch – Apple Support
If the donor device, from which you are transferring data precedes iOS12.4, QuickStart will not be available.
“Transfer” is rather a misnomer. In reality, your data and setup is merely cloned to the new device. Nothing is moved or removed from the original device.
An alternative is to restore either an iCloud or iTunes backup to the new device:
How to back up your iPhone, iPad and iPod touch – Apple Support
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support