Remodeling master bathroom in doublewide. I took out a sink and capped off the water supply and main drain to that sink. Now when I try to get water to work for other sink it leaks and will not drain properly. Is this because the vent is gone to other sink that was removed?

Leaks are not vent related. How far from the old vent is the new sink? If you installed a "vessel" sink, they need a special drain.