If most of my parts are AMD like my CPU AMD FX 8120 and my Mobo Sabertooth 990FX, would AMD Graphics cards gain a boost working with the same company. Like are they tweaked to work better?
No, either brand will work fine with either CPU, any speed differences would be in the motherboard tech which is not really dependent on AMD or Intel. Intel CPUs are better for gaming though.
AMD graphics, motherboards and processors will work together under AMD utilities such as OverDrive and the Fusion Media Explorer, if those utilities are of interest to you.
The Fusion Media Explorer should be rather neat with Windows 8 -- hope they don't screw it up