I need to ask that if we can use custom made android apps and if I want to be able to use it with Samsung smart tv. I have made an app that helps to access various sites from the list that you bookmarked. get instant access to your most-watched websites etc.
You can make remote tuner in Android for your mobile device that will access Smart TV. There are many examples on GitHub.
Smart TVs do not run Android OS so of course you can not run any Android app on a smart tv.
Samsung Developer Program