Fantastic story that and what an illustrious mum you had let alone amazing childhood as I can only imagine. Lovely to think you have that eclectic collection of 78s and sheet music, rather sentimental and special: roll on retirement and getting a suitable turntable a must for sure.
Amateur dramatics a big part of our family growing up, my only claim to fame was being part of Bristol Light Opera Club and having principle parts, which was quite an honor, especially as we would put shows on at the Bristol Hippodrome no less. My mum had her equity card, and did a few professional gigs, 3 seasons with Max Bygraves in Babbacombe and he even came to our home more than once, but I was only young so not really star struck then, but I was mighty impressed by his big black Jaguar. Max wrote a song for my mum which she would perform on stage and he wanted to get Olive (Anna Karen) from On The Buses to do so for TV, but he asked mum first if that was okay, pretty big of him I reckon as he certainly didn't have to of course. I have tried to find the clip on YT but no luck, it was one where the cleaner in a strip club always dreamed of being a stripper, then proceeds to sing about it while going through the act and peeling of several layers of ridiculous garments - quite a hoot.
Another time I remember time I remember my mum telling us about when she had a variety show to do give the prisoners at Dartmoor Prison, and that was with Tommy Cooper amongst others. They were being given a lift down and their ride was in a mini, one of the original types, she was in fits as she recalled being in the back seat with Tommy, who was a big fella of course ... happy days eh?
Might be nice if you came across some of those old thespians and could share some of those master tapes you have, although could involve a lot of work I guess.