The question was "what can I legally hold".
The handguns are a no no I'm afraid. They come under what are known as "section five" weapons, which are prohibited weapons under the
firearms act 1988.
The link should give you most of the information you need, if you have the time to sit, read and digest.
All of the rifles are items that CAN be held on a firearms certificate. They are classed as "section one" weapons (again, named for the section of the firearms act that they come under). However, the fact that they can be held legally, does not mean you will be able to hold them.
In British firearms law, we have this concept called "good reason" to hold any given firearm. We also have universal registration and draconian control on the movement of firearms between individuals and by trade.
Before you can legally possess a firearm in the UK, you will require some kind of authorisation to hold. For a resident this will normally be in the form of a firearms certificate, for rifles and similar weapons, and a shotgun certificate for all shotguns, which are classed as "smooth bored firearms with a barrel diameter of less than two inches"
Now, for firearms held under a section one firearm certificate (basically anything with a rifled barrel that's not a hand gun) you will need to prove that you have good reason to hold that particular weapon before they will grant you permission to acquire that caliber of weapon (ok, they usually state the cartridge rather than the caliber, poorly drafted legislation). The particular good reason that you put forward may limit the uses that you can put the rifles to. For example, if you put down membership of a target club as good reason, then you will only be able to use that rifle on a range. If you have land to shoot over then you may get the rifle conditioned for shooting various species of target animal.
To explain the British firearms law would take many a long page. I'm afraid it will come as quite a culture shock to you after the US. What I've put above begins to give you an idea of the hoops you will be forced to jump through. The whole licensing system is the reason many of us have recommended either leaving the guns in secure storage in the States until you've got the relevant certificates, or bring them over and have them stored at an RFD (Registered Firearms Dealer). If the rifles are held legally in Germany then they should have CIP proofing, which means they can be sold in the UK.
My advice is to spnd as much time as you can reading and familiarising yourself with the various documents that govern firearms, their ownership and use in the UK. Any description on here is necessarily going to be incomplete, and in this could be dangerously misleading. Things we take for granted, a US gun user, used to the much less controlled gun environment wouldn't even think of.
Talking to the shooting organisations is also a useful step. It gives you a knowledgable point of reference for those finer points when necessary, and a voice to help you out if things get sticky.