With the sunsinger's radiance super, you can only buff YOURSELF, not others. The only exception to this is if you spec into the ability that speeds up cooldowns for all fireteam members. So no, you can't stack this super's damage boost (it may be possible to stack the cooldown boost, but we have no way of confirming this as of now) For Ward of Dawn, there's not really anything to stack, unless of course 2 defenders put down both of their wards on the same spot, which would be rather pointless.