I just checked Bond's GENEALOGIES AND HISTORY OF WATERTOWN for your Mixers.Those you mention are listed,but the Joseph MIXER born 22 Feb 1756, son of Joseph and Elizabeth (WHITNEY) is not carried down any further-not even a spouse is mentioned. You probably want to find this book.
Briefly, the lineage is:1.Isaac Mixer and Sarah Thurston2.Isaac and Rebecca (Garfield) Mixer.3.Deacon Joseph and Anne (Jones) Mixer.4.Major Joseph (b 1705) and Mary (Ball) Mixer.5.Joseph (bp 1732) and Elizabeth (Whitney) Mixer.6.Joseph Mixer born 1756.
This info is on pages 367-371.I have found this work to be reliable so far.
Also, there is 1 more generation in England:Isaac and Frances Mixer of Cappel, Suffolk, England Ref:NEGHS REGISTER Vol. 71, p 277.