Swann had a fairly lengthy and at times prestigious career. Way back on the old Vantagenet board, I posted some biographical material I found on him, but no time to re-research and reconstruct that now. IIRC, he wrote a hit play, some screenplays, etc. I think his career peaked and he started doing screenplays for B pics and then soft gothics. He may still be alive (can't find my passwords to check Contemporary Authors at the moment).
Don't know much about Marmorstein.
If I have time tomorrow, I can try and see what I can find out if anyone has an interest.
Frankly, I think both of them were superior writers to Hall, Sproat, and Russell.