From this discussion I have to assume your father has a Mac and an iCloud account and your mother has an iPad and a separate iCloud account.
I'd say log into your father's iCloud account on a web browser, select the contacts in the group, export the contacts (will be .vcf), log out of father's account, log into your mother's iCloud account and import the .vcf file.
If, when you log into your father's account, you don't see all the contacts in question then there's another issue that should be addressed.