Delete iCloud Contacts from iPhone

Curently i have 3 ios devices and three of them are synced to one account only. Now i have given the other 2 devices to my parents. Now the problem is my contacts have been synced with their iphones. Can i know how to delete my icloud contact which is in their iphone. even their contacts too is inside my icloud account. Are there anyways to delete them?

Thank you.