The last thing your german relatives might want to eat is more german food. They will probably be interested in Canadian fare (game and beef) and Native cuisine. That's what my relatives wanted to try.
Wurst is good, more fusion than traditional German. Probably will be closed for months. I believe the German Canadian Club in NE Calgary closed down. Wiener Schnitzel Haus in Montgomery is quite expensive for what looks like a fast food joint in a strip mall.
The Bavarian Inn in Bragg Creek is authentic, but might be closed now too.
http://www.thebavarianinn.com/
6 German Restaurants to Get Your Oom-pah On
http://www.avenuecalgary.com/article...your-oompah-on
Edelweiss, german deli in NW Calgary:
https://www.edelweissimports.com/