You're working on an interesting topic.I know a little about their California years, but was unaware of any connection to the Baja expedition.As to your question about Daniel (W. or M.?), I have always thought the middle initial was an "M" based on the NYT obit you referenced.David M. Chauncey died July 6, 1881, as the July 7, 1881 NYT (5:1) indicates.His brother Daniel M., the other "D.M." died January 29, 1883.The Jan. 30, 1883 NYT obit reads as follows:
"D.M. CHAUNCEY'S SUDDEN DEATH
Daniel M. Chauncey, President of the Mechanics' Bank, of Brooklyn, died suddenly yesterday afternoon about 1 o'clock while seated in a chair in his office in the bank building at Court and Montague streets, talking with County Treasurer Schenck.Mr. Chauncey was in his usual health yesterday morning, and soon after noon went to lunch at his home, No. 140 Joralemon street.He returned in less than an hour, and meeting Mr. Schenck in the outer office invited him to the President's room.Mr. Chauncey had just taken a seat and ligthed a cigar when he threw up his hands and uttered a sharp cry of pain.Mr. Schenck called for assistance, and Dr. J. Lester Keep who happened to be in the bank, went to Mr. Chauncey's aid.Such remedies as could be hastily applied were brought into requisition, but Mr. Chauncey died within five minutes.Mr. Chauncey, with two brothers, came to Brooklyn about 40 years ago.They engaged in the building business, but subsequently went into banking, and were prominently connected with several of the principal financial institutions of Brooklyn for over 30 years.The oldest brother died last Summer.The surviving brother, Michael Chauncey, was completely prostrated yesterday when he heard of Daniel's sudden death.Mr. Chauncey was 61 years of age and very wealthly.He leaves a widow and three grown up sons and daughters."
Daniel's wife was Mary Ann Marshall.Their son, George W. Chauncey (1847-1926), was the most prominent of their children.
You asked if I thought the NY Times might be mistaken in writing "Daniel M." rather than "Daniel W."I don't know but I should believe it more reasonable to think that the NYT got it right, given Daniel's 30-year prominence in Brooklyn.Reading a script "M" as a "W" or vice versa is an easy mistake to make; maybe a momentary mistake was repeated in the San Francisco paper.
David's and Daniel's brother Michael lived on until September 1, 1897.He died at his summer home on Cuba Island, Alexandria Bay, Thousand Islands.Michael's NY home was at 138 Joralemon Street so it would appear that he and Daniel were on good terms, ignoring the upset over the probate of David M.'s estate.
"A History of Real Estate, Building, and Architecture in New York City during the last quarter of a Century" published by The Real Estate Record Association (1898, NY) has the following entry on page 191:
"D.&M. Chauncey Real Estate Co., Limited.
The D. & M. Chauncey Real Estate Co., Limited, is unquestionably the most prominent real estate concern in Brooklyn.The business was first established in 1843, but the present concern was incorporated in 1889 with a capital of $150,000.They combine every branch of the real estate business and sufficient attention is paid to each department that every branch of the business is made a specialty.The members of the company are George W. Chauncey, President; Cornelius Donellen, Vice-President; Ezra D. Bushnell, Treasurer; Thos. Hovenden, Secretary.One may obtain an idea of the business status of this firm when it is learned that the largest appraisment ever made in New York, Brooklyn, or the entire metropolitan district, was made by this company in the case of the appraisal of property bordering on the East River for the Brooklyn Wharf and Wharehouse Company.Their address is No. 207 Montague street, Brooklyn."[It may not be a surprise to learn that George W. Chauncey was elected President of the Brooklyn Wharehouse and Storage Company in 1895.NYT's society article in the March 24, 1895 issue (11:2).
Michael Chauncey's obit is in the NYT (p 7) for September 2, 1897.
Let me know if I can help in any other way.Good luck,