Yes, no problem. The video cards have their own memory controllers and onboard memory that works independently of the system ram.
Most modern gaming build will have ddr3 ram in the system, but gddr5 ram on the video card. They don't need to match.
Post your motherboard brand & model (to be sure you can support dual graphics cards...)
And, your powersupply brand and wattage as well as the model of GPU's your are planning on (to be sure they are compatible with motherboard and each other. And, to be sure you have enough power for them...)