My ancestors (that I'm aware of) fought for the Union -- two of them in the Navy, supposedly -- and I have about 45 flags, about ten of them US Nationals in different patterns, about seven or eight Confederate, half-a-dozen Texas Revolutionary flags and an equal number of colonial-era American flags (like the Taunton Flag and the Continental Flag, the Bunker Hill Flag, and the flag the Green Mountain Boys carried in the Revolution under Ethan Allen and "Mad Anthony" Wayne.
They're all American flags, every one. Not a British or a Mexican or a German flag in the bunch, unless you're counting the colonial flags as "British".
You got Old Glory in there? My ancestors fought for Union too, Army of The Potomac.