A bucket brigade is a type of IC chip that can store voltage levels in each of its little storage cells, and then pass that stored voltage level on to the next cell, and then the next, like a bucket of water passed from one person to the next. Your instrument signal is the voltage, and each time the stored piece gets passed along, it outputs another "repeat" of delay. It's called analog delay, but actually it's in a gray area between analog and digital.
Germanium is an element, and various transistors can be made with different elements. The other most common one is silicon. In a fuzz circuit, germanium is said to have more of a smooth "vintage" tone, while silicon is said to be more cutting and "modern"--but don't take those descriptions as pure fact, only a vague generalization.
"Double germanium" just means two of them were used, for a slightly different tone. There is no generalization to be made about the sound of two germ transistors vs. one, so you'll need to read peoples' descriptions of the specific pedals they're used in. E.g. look for posts comparing the single-germ B:Assmaster to the double-germ one.
