The bended barrel you can straighten up putting the part into warm water.The heat will make the rasin more pliable.When it gets cold the rasin will be firm again. The broken one you can fix using a piece of thin copper wire. You have to bore two apertures with a thin drill bit. One has to be in the borken barrel at the ending it was just broken and the secone one must be in the part of the machine gun where the barrel has to be stuck back. The short piece of the brassy wire has to be stuck into these holes making the joint "stronger". If the broken barrel is beneded as well you have to make it straight with the warm water too, before you will drill a hole in that of course. For gluing you have to use Cyanoacrylate adhesive like Superglue for instance. I would suggest a CA glue offered as a gel. You will have more time to set both pieces at the correct position before the glue can start hardening.
One variation of Wojtek's suggestion on the gel glue. Put the glue on one piece and a drop of accelerator on the other. It wll reduce the dry time but still give you just enough for straightening.