[Svnmerge] Help with somewhat complex branch synchronization strategy

[MrR08040]

Imagine a branch called /A that is branched as /B.  No new changes are
made to either /A or /B.  Then /B is branched as /C.  Again no new
changes are made to either /A, /B or /C.

I'd like to do the following:

A <-> B (keep A & B sync'ed with each other)
A <-> C (keep A & C sync'ed with each other)
B  -> C (keep C     sync'ed with only B)

Here's how I tried doing it:

$ cd ~/svn/wc_A
$ svnmerge init ~/svn/wc_B && svn ci -F ... && rm ...
$ svnmerge init ~/svn/wc_C && svn ci -F ... && rm ...
$ cd ~/svn/wc_B
$ svnmerge init ~/svn/wc_A && svn ci -F ... && rm ...
$ cd ~/svn/wc_C
$ svnmerge init ~/svn/wc_A && svn ci -F ... && rm ...
$ svnmerge init ~/svn/wc_B && svn ci -F ... && rm ...

But I'm not getting what I expect when I use "svnmerge avail" command:

$ cd ~/svn/wc_C
$ svnmerge avail ~/svn/wc_A -b
(nothing printed as expected)
$ svnmerge avail ~/svn/wc_B
(nothing printed as expected - I didn't use -b option b/c it's one-way)

$ cd ~/svn/wc_B
$ svnmerge avail ~/svn/wc_A -b
(nothing printed as expected)

$ cd ~/svn/wc_A
$ svnmerge avail ~/svn/wc_B -b
(nothing printed as expected)
$ svnmerge avail ~/svn/wc_C -b
(prints revision containing "svnmerge-integrated" information)

I wasn't expecting the last line to be printed.  I was expecting
nothing to be printed like the other "svn avail" commands before it.

My question: Can svnmerge be used to do what I want to do?  If so, how
do I do it correctly?

Many thanks in advance.