I have "The Demarest Family', published in 1964 by the Demarest Family Association which outlines all the branches of this family. To keep all the names staight each person is given a number. The first is the generation number and the second is the individual.
Leah Demarest (#3-8) b 1682 m Abram Brouwer. They had a son Daniel Brouwer b 1719 who m Marietje Koning. When Daniel died, his will listed his eight children, two of which were Susanna, wife of Samuel Demaree (#5-56), and Mary, wife of Samuel Demaree Jr (#5-198).
Samuel Demaree (#5-56) b 1746, husband of Susannah, was the son of David Demarest (#4-30) b 1699 and Catherine Van Houten.
Samuel Demaree (#5-198)b 1754, husband of Mary, was the son of Samuel Demaree (#4-84) b 1707 and Leah Demarest (#4-14) b 1713. Samuel and Mary were the parents of Daniel Demaree (#6-402) b 1792 who m Mary Underwood & Ann Lee.
The Demarest/Demarees just loved to marry cousins and in-laws. And everyone had the same names. No wonder you're confused!