Evidence of an evolving city, and evolving/changing attitudes, I agree. It's not a name anyone would choose for a new street today, but definitely historically interesting.

I also think that you're right that Mrs. Mason had a better idea of what Jack was like than anyone else in the house did, at least early on. She probably had enough experience with children to sense something might be off about his attitude towards his baby brother, even before things started to go wrong.

LOL on the ship sinking! You're right that it's a distressingly common way for people to meet their fates in ACD canon.