Other Merge two apk

hi at all,
as the title I would like to figure out how to merge 2 apk in one .... on various guides is explained in a somewhat superficial kind HERE
but they do not explain the manner in which are to be united....

questions and doubts:

1. files in folders 2 apk must be overwritten?
2. in the manifest final go together only activity?
3. into final manifest the package name (ex: package="com.load.settings") This points to the source directory how to bet the other also?
4. the source file into smali directory can be merge within a signe directory?

does anyone know the procedure of how to do?

thanks