In the Watts Hays Letters I've put a list of relatives of Col. Upton Hays and his wife, Margaret Watts Hays who served in the Civil War. Quite a few of these men served with Hays in the MSG and went with the regiment to form the 2nd MO Cav., CSA which was reorganized into the 12th MO Cav. in 1862. Most were from Jackson Co. and a few were from Callaway Co. I have found it difficult to trace the CW service history of the men who left the CSA and became guerillas so find this discussion very interesting and it may provide some information about them for at some point after Hays' death in 1862 quite a few joined the guerillas in Jackson Co. We had a fairly long discussion on this board some time back about who the men were who became guerillas and their motives for doing so. You can view the list by going to the website and clicking on 1861-1865, the Civil War and scroll down to Relatives who served in the War.
I have selected the men I think started with Hays in the MSG or joined him when the Jackson Co. Brigade was formed in late 1861 and men who might have been with Welsh. Some of these men may be part of the group you are studying. I think also that some of these men later rejoined the CSA for Price's 1864 excursion in MO.
Isaac F. Berry Confederate 1st Reg., Missouri Cavalry State Guard (8th Division), Quantrill
James Samuel Berry, Confederate 12th (2nd) Missouri Cavalry
James Berry Confederate Cavalry 12th (2nd) Regiment, Missouri Cavalry, Quantrill
James Tate Berry, Union Osage Co. Home Guards, 2nd Reg., Missouri Light Artillery, 26th Reg., Missouri Infantry
John Edward Berry, Confederate State Guards , 6th Missouri Infantry, Irwinís Reg., Freemanís Co.
Richard Berry Confederate 12th (2nd) Regiment, Missouri Cavalry, Anderson, Quantrill
Richard C. Berry, Jr., Confederate, Missouri State Guards, 2nd Reg
Samuel H. Berry Confederate, Williamís Reg. Cav.
James M. Burris Confederate 2nd/12th Mo Cav., Orderly Sgt., Co. D, Col. Hays; Pvt, Price's Escort
John D. Dickerson, Confederate Cavalry, Poindexter's Regiment, Missouri Cavalry, Pvt., Quantrill
Paul Dickerson Confederate Quantrill
William Hays Confederate 1st Regiment Cavalry Volunteers CSA, Quantrill
Isaiah Jefferson Kimberlin Confederate 12th MO Cavalry, Pvt. Co. D (Shank's Regiment)
Julian N. Kimberlin, Confederate 12th MO Cavalry, 1st Sgt. Co. D
Richard Samuel Kimberlin, Jr. Confederate 12th MO Cavalry, Pvt Co. D (Shelby's Brigade)
William Grant Kimberlin Confederate 12th Missouri Cavalry, Pvt. Co. D
Littrell, Tolbert/Talbot Confederate CSA, Pvt.
Samuel McMurtry Union Co. F. 3rd Reg, Enrolled Missouri Militia and Confederate
Boone T. Muir Confederate Quantrill, Younger
Samuel B. Muir Confederate Quantrill
Daniel Boone Scholl Confederate Quantrill
I'm still working on this list so not all of the information is complete and may not be completely accurate.
Another man, William Overstreet probably served with Hays in the 2nd/12th MO Cav and claimed in an Ex-Confederate Reunion to have ridden with Quantrill. The John Crump mentioned in another post may have been part of this group as Upton Hays' sister Louisa was married to Thompson Smith Crump.
I have a little more information on these men in my files so please write if you have questions.