Best way to handle 2 separate iPhones under (1) account

My father uses an iPhone 12 as his primary phone. It has his personal Apple ID connected to it and uses it for most everything.

My mother has an iPhone 8 which she rarely uses. It has (1) separate email. We would like it to be a completely separate phone (ie. set it up so that it does not link to my primary Apple ID and iCloud account).

What is the best way to handle this? Should I set up a 2nd iTunes Account, a 2nd Apple ID and separate iCloud email?

Thanks