I have 2 Google accounts on my Xiaomi Mi Box S but there is no option to switch between accounts in Google Play Movies. I can't see the purchased films linked to my second account in the app library. For instance, I have no issues on Youtube like that. It works fine.
Any help will be appreciated.
You just need to create a family account and add your second account. Then you just add all your content to your family library and both accounts will have access to all Google play content. This includes movies, tv shows, and apps.
This is how my wife and I share our purchases.
Edit: I should also note that you will no longer need both accounts setup because one account will have access to all content.