Well unfortunately your ancestor in the 7th Missouri State Cavalry Militia would have ridden under the terror that was Brigadier General
John McNeil. McNeil, under Schofield and then Ben Butler. He was largely responsible for the anti-guerrilla weeps through Northern Missouri. Had your ancestor survived to be mustered out in 1864 he would have left under the regimental command of Col. John F. Philips and the brief area command (Missouri and Kansas) of Major General Isaac Stevens (before he decamped to Europe on leave with General Kearny).
As for the one in the 4th Ohio he missed the
Battle of the Rappahannock in TTL. After the battle and Kearny's appointment to command the Army of the Potomac they were reassigned to bolster would have been in the II Division of XIth Corps under von Steinwehr. They would miss the fun along the Rapidan by garrisoning the Valley in the fall of 62. However they would be in the thick of it at
Trevilian Station (by this time the divisional commander Milroy has been replaced by Devens). Of the three divisions in the XI your ancestor's got off the lightest.
At
Ashland the II Division would follow the I under Barlow but again not see the worst of it.
They played a significant part in Kearny's
feint at Richmond. After Richmond Max Webber would take over command of the division from Devens who reverted to brigade command. The biggest day in their life might have been the third day at
Gettysburg. If he survived Meade's uphill charge at Wolf Hill as part of Devens Brigade he was a very lucky boy. As a result of this beasting they mostly sat on the Trevanion Road at Union Mills/Pipe Creek...
XI took a holiday garrisoning Virginia under Sedgwick in which role they would see out the war no doubt to their delight...
12th United States Infantry - I don't suppose you know when his short stint occurred? His service might be butterflied into another regiment after the POD.