You are correct! Here is a M12 Gun Motor Carriage in action in Aachen.

I am having a hard time finding the quote (so take it with a grain of salt), but I recall a German commander in Aachen saying something along the lines of "when the Americans begin to use artillery as sniper fire— you have lost."

From what I've read, the Germans prior to the battle had pulled civilians out starting with children. It was noted that they simply dropped a bunch of kids off just east outside of the city. They later rushed in and began escorting out elderly and women— who were horrified to see the soldiers immediately fortifying their houses with concrete and such as they were escorted out.

That's not to say there weren't civilians left in the city. It's interesting to note that Hitler had ordered the evacuation of the city because he suspected the population preferred American occupation because allied bombing would cease. Generalleutenant Gerhard Graf von Schwerin had paused the evacuation and appealed to the allies to treat the populace "mercifully". Word got out to Hitler that he did this and ordered him arrested— but surprisingly forgave him later. As far as I know, the Germans resumed the evacuation of civilians and that it was enforced pretty "harshly".

That is really interesting. Speaking of the werewolf teams, which I believe were the idea of Otto Skorzeny (I could be wrong), there were a few instances where allies found cables strung across the road intended as a trap for jeep crews. This lead to them placing posts at the front of the jeep such as this one.

Your grandfather took part in a historically significant battle. White phosphorus grenades and flamethrowers were also used. The allies used AP rounds to shoot through floors and ceilings and would make a dash to the top floor of a building and work their way down— forcing the Germans into a basement. The allies found it safer to shoot bazooka rounds and use explosives to blast entryways known as "mouse holing". This lesson was learned and applied later by soldiers engaged in urban combat in Vietnam— even today as noted in the Baghdadi compound raid.

The German force holding the city was about 18,000 strong. Some of the personnel used as infantry were originally Kriegsmarine intended to crew U-boats (funny how history rhymes, given the use of Navy crews by Russia).

Straight to the top. The first German city taken by the Allies. Very intense urban combat. The Germans had a habit of hiding in and ambushing from basements— so Shermans would blast houses starting from the bottom and up floor after floor. One round was said to have gone through three houses before exploding in the fourth.

(Not so) fun fact: German civilians were afraid to evacuate to Cologne because there was a rumor that the Allies had dropped biological weapons there.

Aachen doesn't get much coverage, seeing the pic brought into frame made me very happy.