Separating iPads.

What you do next will largely be determined by your future intentions for your old iPad...

Having transferred all your data from your old iPad to new, if you wish to completely erase your old iPad in readiness for a new user, this procedure might be the most appropriate:

What to do before you sell, give away or trade in your iPhone, iPad or iPod touch – Apple Support

This procedure will erase all data and settings - and remove the Activation Lock. It may then be sold, given away, or just set-up again as new - as you so choose.

If instead you intend to continue using the iPad - but do not wish content/data to be synchronised by iCloud - you can disable any services that you do not wish to use from Settings on your various devices. Consider that if you also use an iPhone, you’ll need to be selective as to the device(s) upon which services are disabled:

Settings > [Your Name / AppleID] > iCloud - select or deselect services as needed

if you want to change appleID on one of them

https://www.laptopmag.com/articles/how-to-change-apple-id-ipad

if you just want them to automatic install new apps that has been purchased or downloaded with the appleID then

Update apps or use automatic downloads - Apple Support