Here's something to get going with!
The photo of your wife's grandfather shows him to be an army (Heer) private. I can't quite make out the number on the shoulder board, but if it's a '64', then he will have served with a regiment of that number. The colour of the piping on the tabs on his collar would determine the branch. They don't look white (infantry), but if they are then he could have been with Infanterie Regiment 64:
http://www.lexikon-der-wehrmacht.de/Gli ... r/IR64.htm
If they're red, he might have served with Artillerie Regiment 64:
http://www.lexikon-der-wehrmacht.de/Gli ... g/AR64.htm
The white stripe at the shoulder end of the shoulder board probably means something too - I'll have a look in a book I have and get back to you tomorrow.
As a guess, I'd say the group shot was of a student club with Nazi affiliations, two of whose members appear to be in the SA.
In the first photo, you have two Heer officers, taken, I'd say, pre-war.
The best course of action to determine your opa-in-law's military service is to submit a query with the Deutsche Dienststelle (WASt) at their website: http://www.com-de.com/wast/
You'll need his date and, if possible, place of birth. It takes about six months for a reply.
Also, if you have any Feldpost numbers from letters written by or to him during the war, these can be decoded and will give the unit he was with. The numbers are five digits long and could be hand-written or stamped on the envelope.
In the meantime, I'm sure there are lots of Feldgrau members who'll be able to pick out more info for you from these three photos!