Our Abigail was not Abigail Mattern. Abigail Mattern was married to John Betle/Bedle/Beedle, and Quaker records show their marriage date as 1698. Abigail Siddle had already given birth to a second child, Martha Siddall, who was born in 1696, well before that date. Refer to this article for evidence.
Henry was deceased by age 10 in 1704 when his father made his will. I have no information about him except his birth, which was recorded in Quaker records.
There is a Quaker record of Martha's birth on the date given. This date would correspond to 3 July on the new calendar. The document also has a record of her marriage to Samuel Harker. I have not attempted to follow their family.
A burial record states that Alice, daughter of John and Abigail Siddell, was buried the 16th day of the 8th month in 1698 (old calendar).
I have found no records for John after appearance in his father's will.
Abigail too seems to have no Quaker records after 1704.
Married Abigail about 1693.
From the record shown on the page for John's parents, we know that he and brother Henry came to Pennsylvania as servants in the family of Henry and Margaret Baker. Since the Baker family was from Lancaster County, the Siddles were likely from there also.
John made a will day 9, month 2, 1704, and the will named all the children except Henry and Alice, who were deceased by that date. The will also referred to Abigail's "being with child at this time."