If you are using the iCloud Photo Library, you have no photos that are "only on the iPad". iCloud Photo library by definition syncs all photos in the Photos to iCloud, and keeps a local copy on the iPad.
You can turn off iCloud Photo Library in Settings ➜ Photos, and then delete them from the iPad. doing this will prevent the deletions from affecting the other devices using the iCloud Photo library.
Alternatively you can turn on Optimize Storage in Settings ➜ Photos to reduce the space used up by the Photos on the iPad.
click here ➜ Manage your photo storage - Apple Support