Ubuntu source package dependency tree

You would use a Makefile with the build dependencies declared, for example as follows:

default: A.deb B.deb C.deb

C.deb: B.deb C.dsc C.tar.gz
        <command(s) to build C.deb>

B.deb: A.deb B.dsc B.tar.gz
        <command(s) to build B.deb>

A.deb: A.dsc A.tar.gz
        <command(s) to build A.deb>

Note that the command indentation is a TAB.

With that Makefile, you would use the command

make

and this would work out which packages to build and in which order, and then build them, all depending on the timestamps of the files. E.g., if say B.tar.gz has a timestamp later than B.deb (i.e. package B has new source), then that'd cause firstly B.deb to be rebuilt, and as that would make it be stamped later than C.deb, it would cause C.deb to be rebuilt as well.

Well, maybe I'm totally missing your point, but it sounds like you're recompiling package A and want to recompile packages B & C, wich I would simply us a makefile for.