Yes, I see that at first glance it looks like Maria Schoonmaker that had been married to William Jaycocks could be the widow Hacker and sister of William Henry Schoomaker "brother of wife".
However, I just found this listing:
New York City Marriages, 1600s-1800s Name: Maria Schoonmaker Spouse Name: William Jaycocks Marriage Date: 1814 Marriage Place: Poughkeepsie, Dutchess, New York
This listing indicates that Maria Schoonmaker married William Jaycocks, just two years before his death in the year 1814.
When Capt Hoysted Hacker's first wife, Mary Elizabeth Calder, passed away 9 Feb 1794 in NYC, (looks like shortly after the birth of son Hoisted born about 1793) the Captain would have needed help raising the young children. Sons Edward and William were born in 1805 and 1809 and they were defintely Mary Jacocks's sons as they were born after the first wife's death. So the dates for Maria Schoonmaker don't line up.
New theory - Thomas Jaycocks left the will dated 2/20/1817, probated 3/27/1817, in which he states his heirs as Sarah M., Hoisted, Edward and William children of Widow Hacker of New York.This is the basis of the speculation that "widow Hacker" could be his sister. Since Captain Hoysted Hacker was born Christmas eve 1743, it would be unlikely to have a wife from the generations after Thomas Jaycocks. The reference to Shoonmaker works against this theory unless it is vaguely referrring to someone else entirely.