I agree, the first one is certainly a bobbin. - In my (new-ish) Brother sewing machine the bobbin is wound with thread on a special bit on the top of the machine, just to the front and right of the main spool holder. You put the bobbing on and push it to the right till it clicks. From what I remember of my mums old electric Singer, it was the same... it's probably a standard size for electric sewing machines, the old ones I had all fit my new machine.
The bobbin sits inside a metal case which has a handle on it and a screw at the side which is to adjust the tension. This case fits into the lower part of the machine -through a small access panel in the front, just under the needle. The needle at the top, when properly threaded, drops through the hole, wraps the thread around the lower bobbin and pulls the bottom thread up and through the hole at the base of the sewing platform.
The holes in the top and bottom disks of the bobbin are to assist in the winding of the spool - you push the end of the thread through the small hole and hold the end of it while you let the machine wind the thread round.
It could well be different for treadle machines, I have never used one.
As for the other 2... I don't know
They might be for specialist sewing, number 2 looks like it might hold something at a strange angle... could be for leather stitching - bags and belts???
I have many odd bits for my machine, button holers, double stitching bits,etc... but I had the instruction manual, otherwise, I'd never had guessed what they were.
I didn't mean to write a thesus on it

, it is pretty difficult to explain without just being able to show someone, but I hope that helps.