It is important that Orser's tracing their family history do NOT just look at printed genealogies and look for primary searches.In the early years there weren’t computers and everything was typed.People made a lot of typos.Mistakes were made and the mistakes were copied over and over again.This is very common.Researchers do not check out primary sources they just copy what they have found assuming that the info is correct.If you search the records of the Old Dutch Church in Sleepy Hollow, NY you will see that Joseph Aertse (Orser) was baptized August 27, 1723 (not 1725) His father is listed as Aert Aertse and his mother is Mary. Other children of Aert and Mary (Maria) are also baptized there in 1718 and 1719.Baptism dates do not mean they were all babies when they were baptized.Note that Elbert, Jan and Grees were all baptized the same day.All records should be checked to make sure printed genealogies are correct.Sometimes there is no real proof and researchers say what they believe to be correct.I believe that Joseph's mother was Mary Mott.I came to this conclusion after much research.I am willing to change my opinion if better proof comes to my attention.
Here are some genealogies on the Orser family
Orser by Daniel Turner is the only book that lists ALL Orser families. This book is out of print but the LDS can get you a copy.
Another source of Orser genealogy can be found in the article Aert Willemszen and his Descendants.
This article was published by the NYG&B. The article is in their July 1895 issue. It is by Robert B. Miller.
Also check out Grenville Mackenzie’s manuscript Aertse, Arser, Orser.
"Mackenzie" refers to a typed manuscript called "The English Families of Philipse Manor in Westchester County, New York" by Grenville C. Mackenzie He was a professional genealogist who assembled this work over a period of years treating each family in a separate set of pages. You can write or call the WCHS to get a copy
Westchester County Historical Society
2199 Saw Mill River Rd.
Elmsford, NY 10523
You can get a copy of the Aert Willemszen article from NYG&B
You can find the Old Dutch Church births and marriages here