Welcome @aggoro ! 
Have fun reading! I think you’ve picked a good book to join, it’s pretty fun so far. It does spoil some of the murders of the previous main entries, but… Not in much detail, luckily.
I think you mean the other brother. I’m not actually sure how to read his name. Is it Sukechi?
I had the same thought! But then to see that someone called 猿三… What if it was 金田一 looking for clues in the abandoned house, and he’s now laying a trap for 猿三…?
Whoops, yes, I meant Suketomo (in my copy this is furigana’d on page 11).
Yokomizo Seishi don’t rape women challenge (IMPOSSIBLE)
I keep reading ahead without posting anything, then can’t remember what exactly happened in each chapter 
.
But anyway, I still like the book, though I’m not putting much thought into the mystery this time. Probably because the mystery is more “who and why” rather than “how.”
I was surprised by 佐智 here for the reasons we were discussing when 佐武 was similarly awful, but it made me belatedly realize what makes the will situation especially so grim is: while to our perspective not being awful rich dudes in the 1940s, it’s at least up to her which to choose to marry one of these bad options or not - to the awful rich 1940s dudes it’s “she has to marry me or she loses a giant pile of money.” Especially now that one of the alternatives is dead and the other apparently disfigured.
The entitlement and assumption she’d see his way one way or another seemed unpleasantly realistic.
Completely separately, I liked the lonely reed-surrounded wreck of the old man’s old house in the river delta a lot as a setting.
I wonder if rule of threes means this kind of thing is going to happen one more time with 佐清? I do also assume 佐智 is toast, thankfully. I guess if so, the remaining outcomes inheritance-wise are 珠世 marries 佐清 and gets everything, or she doesn’t and 佐清 gets the remainder… or 静馬 is found and gets all or most of the remainder if anyone else dies or those two don’t marry?
Speculating… I wonder if it would make any sense at all if 佐清 is the mystery man who intervened here, and the one who passed the print comparison,
while 静馬 is the one who’s disfigured? That would mean 静馬 would be the one searching for something in 珠世’s room (then knocked out, with a second swap made by 佐清)… and he would have a reason to! The watch has a fingerprint of what in this far-fetched scenario would be 静馬’s, which could still be compared to reveal this convoluted ruse. But the knockout and 松子’s surprise make it unclear weather anyone involved in this hypothetical scheme is actually cooperating with each other, which wouldn’t make a lot of sense… and the motive remains unclear also. But I suppose overthinking possible harebrained mystery novel schemes is part of the fun when I have all these notes to draw on…
P.S.:
Alas, my muscle memory from writing it down a bunch is sad to report it is 猿蔵
Chapter 6:
Looks like I was right about the 斧琴菊 themed killings. The bit about the ropes having been looser then tightened was interesting; it suggests we have two or three people involved:
Obviously 2 and 3 could be the same, but it’s curious that the koto wire wasn’t just used as the murder weapon. Wasn’t there something about the other guy being stabbed with a different kind of weapon to that was used to take his head off too?
