How to create android activity layout design that can support different screen sizes and api's?

I am currently working on first Calculator project. I am facing an issue in designing the UI, I need few of the buttons of UI to have span of 2 columns/rows, so I took help of Grid view layout for this. But after designing, the layout disturbs in different API levels, for instance I am working on API 22 it has different organized look, but in API 16 button shapes changes and view disturbs.
What could be the solution for it? Any attributes to set? Or we have to create different apk's for such...

How to create android activity layout design that can support different screen sizes and api's?