The idea is how to build an android game that contains inside it many small games like Snake, draw letters, Sudoku...(Elevate as an example)
Should I use Android native, ionic, unity…?
Note that Elevate has incredible animations. Elevate in Play Store
I'm almost certain it's a native app based on the standard UI widgets (e.g. RecyclerView, CardView, CoordinatorLayout) it uses.
With that being said, you can surely build such an app with other tools like Unity or even Game Maker Studio. However, implementing UI widgets that mimic native Android functionality can prove difficult and time-consuming.
My recommendation would be to use an IDE such as Android Studio and utilize Google's vast UI libraries to build the menu sections of the app.
As for the mini-games, it all comes down to managing resources and memory (making sure that resources for a particular game are loaded in/out of memory as needed).