Sharing Apple ID with 2 iPhones

Hi. I’m about to start my 81 yr old Dadon his first iPhone. My Mum, slightly younger got hers last year.

Ideally I want them both using same Apple ID. They share an email address and frankly, the idea of having to set up a second email for my Dad makes my blood run cold. 😂

I know this is not ideal but it’s the easiest less stressful option.

Are there any major downfalls for this?

TIA