WHL Wallace's Brigade was not the first brigade hit by the Confederate breakout attack on the morning of February 15th, 1862. The first brigade was John McArthur's (9th, 41st, 12th Ill) posted on Dudley's Hill with some companies of cavalry between his flanks and the river. This brigade was Union right flank. The next brigade in line was Oglesby's (18th, 8th, 30th, 31st Ill) and then WHL Wallace's. The 11th Illinois of Wallace's Brigade was his right flank regiment along Wynn's Ferry Road.
They suffered over 50 per cent casualties in the battle that day especially when being hit by Forrest's cavalry regiment from one side and the 2nd Kentucky Infantry (CS) from the other. 62 men dies at the crossroads they were defending. These men are the first graves at the Ft. Donelson National Cemetery.
If the 26th Tennessee captured flags that day they came from either McArthur's brigade or Ogelsby's, the latter breaking when hit from the front by large Confederate reinforcements after McArthur's retired from being out of ammo.
One of the hats that I wear is president of the Friends of the Ft. Donelson Campaign and I give tours of this site all the time.