If you wanted to see any of my books to see if the 3 January 1864 killing of your Adams ancestors are in one of them, don't bother, they are not. I have not heard of this incident before, and it's not in any of my writings. I am writing of guerrilla operations in 1864 now, and this incident is not in it. That being said, let's look at the facts and see if we can figure who may have killed the two Adams men and mortally wounded the third.
By the way, I see in the 1860 census of Spring Creek Township of west-central Howell County that there was also a William J. Adams living near the Benoni Adams household and the Edward L. Adams household. Where was William J. Adams when this killing was done?
I see in an old Missouri map that Pottersville is about 10 to 12 miles southwest of the county seat of West Plains, so I now have the lay of the land that will help me in my calculations.
I don't know if Captain William Monks or his men killed your Adamses. Monks was still detailed to the 6th Provisional Enrolled Missouri Militia (PEMM) and evidently still operating out of Pulaski and Phelps Counties as of December 1863 and January 1864. It gets confusing since Monks' unit, the 6th Provisional EMM was converted to the 16th Missouri Cavalry Regiment at about this same time. It is possible that Union troops from the large Rolla, Phelps County, base raided the Adams' homes in Howell County.
I think it is more likely the troops that raided the Adams' farms came from a base closer--at Houston, county seat of Texas County. The Union troop disposition report tells me that the small Houston garrison was manned as of 31 December 1864 by Captain Richard Murphy and Companies B and G of the 5th Cavalry Missouri State Militia (MSM) and Captain A. McKinney and Company I of the 6th PEMM. Captain Murphy was the garrison commandant of Houston. Of course, McKinney and his company were part of the same regiment as William Monks. Both the 5th Cav MSM and the 6th PEMM were know to "shoot first and ask questions later" and were also notorious for shooting prisoners "trying to escape." If Murphy or McKinney or their men gathered information that the Adams of Pottersville were "notorious Rebels" and guerrillas it is highly likely that a group of one or both of these units was sent to Pottersville to deal with them. It is also likely that this was purposely left out of the records of the Houston garrison. I don't recall seeing such a record, but some northern units didn't keep records of "more questionable" patrols. Lieutenant Boyd of Captain Murphy's garrison wrote such a report about lots of house burnings and prisoner shootings on a patrol 4-9 November 1863 and it raised a great stink in the Union command of this district and at the state level. Patrol leaders from the Houston outpost quickly saw that they should omit certain activities from their reports from then on.
That's about the best I can do for you. That is my best guess. It isn't much, but perhaps it will help.