Generally, amazon prime and netflix comes pre installed on Android TV. Only then they will support 4K HDR (due to some device certifications and DRM issues). Amazon prime and netflix installed via playstore or USB may not stream high resolution videos
Amazon Prime app for TV is not available in Google Play Store. They have restricted the same to few premium models (Sony, LG & Samsung and may be Pana), where it comes normally pre-installed or thru the OEMs appstore. For other TVs they can access Amazon prime thru fire stick (cost around 3999/-) available at amazon.