How to delete photos from iPad without deleting from paired iPhone?

A request to delete a photo from any device participating in iCloud Photos is a request to delete them from that device, iCloud, and all other synchronized devices.

So NO! If that iPad is participating in iCloud Photos, it would NOT be safe to delete your photos from it.

----------

You can turn on "Optimize iPad Storage." This gives the iPad permission to substitute low-quality, space-saving copies of photos for full-size ones. There is no manual control over this substitution - it is completely under the iPad's control as to when to replace full-size copies with reduced-quality ones, or vice versa. (The idea with this feature is that iCloud always stores full-size copies, so an iPhone or iPad that has substituted reduced-size ones could re-download full-size photos, on demand, later.)

You could also disconnect the iPad from iCloud Photos so that it does not synchronize against iCloud Photos at all. Once the photo library is strictly local and is no longer synchronized with iCloud or other devices, you could delete photos from it without affecting the copies on your other devices. But you would then need to make some sort of backup provisions for whatever new photos you took on the isolated iPad – and if you wanted to move new photos from the iPad to them, or vice versa, you would need to so manually (e.g., by exporting copies to iCloud Drive or by e-mailing copies to yourself).