Want to watch the same show on 2 different Roku TVs

Rentals are available on one streaming device at a time. It is permitted to download (and play) one copy on mobile or computer, and stream on one other device simultaneously. Rent movies from the Apple TV app - Apple Support (paragraph Watch your rental on another device).

The rental will be available on your account until it's expiry (30 days to start and 48 hours once playback begins). Make sure you are signed in with the same ID, can also refer to the article below.

Rent movies from the Apple TV app - Apple Support