There is very little information available on Manson's children. I have found a couple different scenarios for Charles, Jr.'s suicide. One claims that he shot himself in his car somewhere in Ohio. The other claimed that he hung himself in a closet in a hotel, no location given.
As to why he felt suicide was his only option would be guesswork as best. It would not be surprising to find that he suffered from depression or other mental illnesses, considering the gene pool he came from.
1870
June 9, 1870
Patrick Manson died in 1922.
Maurice Manson died in 2002.
Andy Manson died in 2009.
Ray Manson died in 2004.
George Manson died in 1876.
Manson Benedict died on 2006-09-18.
Frederick Manson Bailey died in 1915.
Rufus P. Manson died in 1897.
Héléna Manson died on 1994-09-15.
Alexander Malcolm Manson died in 1964.