Fortunately the Adams and Westons were homebodies. It looks like most of them lived almost their entire lives in Irwin. A good thing because the surname Adams is rather common.
John and Mary appear in the 1880, 1900, 1910, 1920 and 1930 censuses in Irwin. He was born June 1856 and she in July 1856. They were married 21 years.
The 1870 census for Irwin shows a John Adams 14 with William Adams 44 and Mary Ann 43. The family is also there in 1860. I could not find the family in 1850 anywhere. William and Mary also appear in the 1880, 1900 and 1910 censuses in Irwin. He was born Nov 1824 and she in May 1825. They were married 52 years.
A Mary Weston 14 appears in the 1870 census with George 59 and Ann 47 in Irwin. The same family appears in the 1860 census living next door to the same William Adams Family above (looks like John married the girl next door). George and Ann are also in the 1880 census in Irwin. I could not find them in the 1850 census.
Some of these records you can look at for free at labs.familysearch.org and Ancestry.com. For those you cannot see for free I suggest checking with your local libraries to see if they have Ancestry or Heritage Quest.
I suggest contacting the Venango County Genealogical Club and Venango County Historical Society to see if they can help you with obituaries and other data. I also suggest getting the death certificates for each person in your line going back.