Bob,
Thanks for your reply. I am, first of all, the Ken S. from the GWF, so apologies for not making that more apparent. I suppose it would have saved you from making a long reply.
If only I had any such documents... My grandfather apparently kept up quite correspondence with my grandmother, but if it survives I have no idea. When I visited my aunt in Germany she only made vague reference to "papers" but I don't know what they are specifically; she apparently didn't trust me to go through them.