Need Help about RAM

I dont know allot about that but I think yes it can be a from a different manufacturer.

It can be from any manufacturer but it needs to be the correct type for your motherboard, you should also match the speed of the current RAM or you may run into issues.

Nope , if u have mb with dual/quad channel and in your mb documentation is specified "8/16 gb support" will be fine.

as long as your board supporting dual rams, "most likely" you'll be able to use another 2X4gb or 2X2gb set of dual ram. all you have to do is install identical rams n same slot (like slot 1: old one, slot 2 new one, slot 3 old one, slot 4: new one). And also you should buy rams on same frequency with rams you already have(most of rams in higher freq able to works as lower freq too, however it's a risky crap, you'll never known till test them). however this is only how works n theory, i strongly advice test it first before pay them or ask a guarante in case they wont work.

ok thx for ur help