I'm no expert either....
Yes there is something known as pigtailing......but IIRC it refers to 'multiple wires' being 'twisted together' with one wire so that that wire can lead to the (outlet/socket/fixture/switch). It is done so that there is only "one" wire connected to the item. IIRC there is a limit as to how many wires can be twisted together with the one wire....

Now about the aluminum wiring.....from what I've read and been told by several electricians......DON'T PLAY AROUND WITH IT!!!!

They've told me things that (unfortunatley) I can't remember the details of....but I remember that I decided I won't touch it. Now I am NOT an electrician but have worked on may electrical projects and a number of them were on 220 lines...and I remember that what they told me basically led me to think that I didn't want to deal with the stuff.....if anyone knows more or better than I then PLEASE say so.......I'm interested too....