Thank you for pointing out the Miller Co. Museum marriage database. I'll have to look into that. I noticed that there were 4 John Witt marriages listed but only one of the John's (much too young) is still in Miller Co. in 1900.
Are you sure that you want to claim that Arthur G and John Witt were brothers?
They certainly knew each other and the families intermarried and they were both from TN via Sangamon Co., IL. Of that there is no doubt.
But the John Witt (I don't see any record of him being called Jonathan) and married Frances "Fanny" Coker and went to Miller Co. was the son of Revolutionary War soldier Jesse and Ruthy (Witt) Witt. There is extensive DAR information and articles published on Jesse Witt. I am not aware of anyone claiming that Jesse Witt had a son named Arthur. You might check the DAR files to be sure.
Jesse did have a son Jonathan Mulkey Witt but he stayed in Knox/Warren Co., IL until after 1880 when he went with some of his children to Harrison Co., IA where he died 13 Jul 1894 (Logan Cem. records).