It looks to me that you have a few different people here.
The certifiate in image 1 was issued to Wilhelm Hepp in 1871.
The second image if of a Prussian (not Bavarian like Wilhelm) corporal who was in infantry regiment 70. He was a musician- you can tell this by the "swallows nests" on his shoulders. The picture was taken after 1888. IR 70 moved to Saarbrücken in 1887, but the small picture of a young Kaiser Wilhelm II. in the bottom left corner tells us that it had to be after Wilhelm II. became Kaiser in June 1888. So, this phoot is certainly not of Wilhelm- perhaps a son???? But if so, why in the Prussian army and not the Bavarian like Wilhelm. Also, the certificate in image one states that Wilhelm came from Odenheim. The only Odenheim I can find is in Baden-Württemberg, a bit NE of Karlsruhe. That's a puzzle. Any idea about Wilhelm's life after the 1870/71 War??
I have a list of all military musicians in 1899 and there is a Heinrich Hepp in IR 115 in Darmstadt. He played bassoon and violin. Not sure if he is the same man pictured in image two, but I tend to think not, as it is a different regiment and both were very junior enlisted soldiers.
The third image is not detailed enough to draw any definative conclusions. But he looks like a cavalry soldier due to the sword he is carying. The cross could be any number of medals. That the band from which it hangs is painted in the same color as the medal is rather odd. As far dating it, I can't even make a guess.