As far as the route goes it'll be, lahore-peshawar motorway (M2 & M1), and you'll exit from RASHKAI/MARDAN, follow N45 malakand-dargai-kabal and get onto N95 for Bahrain-kalam. For directions you only can ask anyone at rashkai and malakand for bahrain it's almost a straight road and you'll iA have no problems in that regard.
Well August is the most flood affected month of the year. So there's always a chance of the water level rising. But according to the locals it usually is non catastrophic. The 2010 flood was something unusual, that happens after about 12/15 years. But it's better you consult someone knowledgeable in this regard.