When you install a package:-
1) We find the package you ask to install in the current source
2) For each dependency, we look for it first in the current source. If we don't find it, we look for it in all available sources (in no particular order). The first source that has the dependency wins.
In your case, as long as you have the official feed listed and enabled, installing packages from your local repository should get you dependencies from the official source.