That the date of this photograph might be determined from the old car is not beyond consideration, but I have not found a good reference to identify its model year. The spare tire cover reads "Downers Grove Hudson-Essex Sales-Service" and Downers Grove is a Chicago suburb near May's house back then. Essex started making enclosed sedans in 1922, and this is probably a 1925-1926 model.
Most likely, George's sisters May Brown and Alice Cowlin had driven down from Chicago with some help from brother-in-law Lou Cowlin, while sister Dora Bremercamp and her husband Walter had come over from Tulsa for a visit. Dora is not in the picture and is, perhaps, the photographer.
Baby Marjorie (b. 1923) is not in the picture and is, perhaps, napping.
The details of the oil-field house porch are interesting. Note the birdcage hanging from a rafter towards the rear and the wringer washing machine.