RAM and Motherboard compatability is typically based on the RAM being equal (same make, model, timings... Etc) to have the greatest compatability with the motherboard. If the RAM is different, it runs at the lowest speeds and you have a much higher chance of BSOD. I wouldn't recommend adding your brother's RAM to your PC.
More if u want install it in the rig that u have in ur sig u won't see any performance increase since that mobo and CPU don't support tri-channel RAM and even for tri-channel configuration the RAM must be equal size, CL and voltage.