I am the son of Bertram Dench, and the nephew of Sidney. Ethel was my father's first wife. I'm intrigued by your post because, to the best of my knowledge, Bertram never went to America, and I don't think Sidney did either (I don't know about Ethel).
I'd be very grateful if you could get back in touch with me via email. I have a large collection of my father's theatrical material, and am always interested in finding more pieces of the jigsaw puzzle that was his long acting career!