I can’t watch the movies my father bought

You have not mentioned where did he buy the movie --> If you don't see your family's shared content - Apple Support

Buy or rent a movie or TV show

1. In Videos, tap Store.
2. Tap an item to see its details.
3. Tap the purchase or rental price.

See Manage your iTunes Store purchases and settings on iPhone.

Note: iTunes movie rentals aren’t available everywhere. See the Apple Support article App Store, iTunes Store, and Apple Books availability