Hi, I know you want to make simple app with your requirements, I have checked your specs, and I can think it's not simple actually.
1. The app must have sign in/up function for 3 users.
2. 3 users have their roles to upload videos, watch, be available to accept the video posting, vote.
3. Integrate with firebase database for user registeration and video uploading.
4. Show/remove ads on video player with subscription.
I would like to discuss more details with you.
Thanks
Ivan.