Load management for a multi-subcontext application

I am developing an application containing a large number of functions divided into several independent subcontexts. Let’s say I have a main context Main’ (defining a few general symbols to be used in all subcontexts), and subcontexts Main’A’, Main’B’, and Main’C’ in respective files Main.m, A.m, B.m, and C.m residing in the Kernel subdirectory. I want the application to behave like this when loading:

<<Main`

loads everything, i.e. Main’, Main’A’, Main’B’, and Main’C’ when invoked from a fresh session. Each subsequent call to any subcontext reloads that subcontext only (or nothing if called using Needs). But when a subcontext is loaded from a fresh session, e.g.

<<Main`A`

only main context and Main’A’ are loaded. Subsequent calls to subcontext load/reload called subcontext, but subsequent call

<<Main`

only loads those remaining subcontexts that have not yet been loaded (or none if all were separately loaded).

Is there anybody who can help? Thank you in advance.