What kind of guns they're using? (the HK cops)

I'm pretty sure those are the Glock 17-20, it's kinda hard to tell which exact model though. Very reliable weapons, and used frequently by different police across the world.

The HKPD uses a couple of different handguns. The normal beat cops use a .38 caliber Smith and Wesson revolver, and have since, i think, the early 80's. they are beginning to transition to the Glock 17 (parabellum, 9x19) 9m handgun, which is what the HKPD Inspectors use. The Glock 17 is, by great lengths, the most commonly used law enforcement pistol today. They use an assortment of other arms depending on the situation, but in answer to your initial question, its a Glock 17 (which is famously easy to field-strip and clean, as are all Glocks).