I set-up a new IPAD using my Iphone. How do I set-up using my existing IPAD also?

You can only restore from one backup. I’d pick the one that has the most on it that you want on your new device and use that.

Then for the apps not in the backup you can download them to your new device and then see if you can get info onto it. For example if a game has its own cloud save mechanism or account then you can sign in and perhaps get your data on the new device.