I also think that Jellylorum's kittens are Electra and Jemima. Jemima is kind of the off one, so she could be Jenny's kit. Electra looks like Jelly and Skimble a bit, though.
I don't think that Gus could ever be Jelly's mate, but actually her father. That could be why she sings to him more in the way of someone looks up to someone, not like someone she loved like a mate. She also seemed to know all of his stories, so maybe she got to act in his plays.
Skimble and Jelly always seem like they're together. Electra is probably a late daughter, and Demeter is their first daughter. That's why Demeter is older. Demeter, in her golish costume(Movie) reminds me of Skimble and Jelly put together. But that wouldn't work for Bomba and Dem, unless they were half-sisters or just cousins.
Haven't you also ever looked at the costume simularity between Macavity and Bombalurina? Looks the same in color. That may be a reason why she knows about him.
Well, what do YOU think?