When one is alpine skiing, it feels much safer to ski in a crouch than to ski upright. Try tucking and building some real speed, then stand. It's scary. So yes, being lower on the bike does feel safer, because it is less far to fall, and in fact it is safer. Not that we should all ride around with slammed seatposts. We set our saddle height in relation to the pedals for pedaling efficiency.
BB height is determined by use. CX and mountain bikes will have higher BBs. Road bike BB heights are set so that with standard crank lengths, we can go around ordinary corners while pedaling.
Weighting the outside pedal has nothing to do with changing CG. It's purely for skid recovery. If one's weight were in the saddle when cornering and the rear slid out, one's butt would go to the inside, increasing lean angle and bringing one down. With the weight in the pedal, the outside foot will follow the skid, possibly allowing one to steer into the skid and simply drift the corner a bit.
COM and COG are the same thing.
Since one has to lean a bike to corner, one has to accelerate the CG toward the center of the corner and then back out again. We frequently do that by countersteering - moving the contact patches toward the outside of the corner - thus allowing the acceleration of gravity to move our CG toward the inside of the corner, with our contact patches as the center around which our CG rotates. So yes, the closer our CG is to our contact patch, the smaller the distance through which our CG must move, and the quicker we can enter and leave a corner. That said, quicker is usually perceived as the opposite of stability.
One sometimes sees singles riders drop their bike into a corner while holding their body more upright. This enables them to drop in and out of a corner faster, though it increases the angle at which their tire contacts the road surface. This is probably not an option on a tandem.
Dropping a knee to the inside moves the rider's CG to the inside, thus slightly decreasing the angle of lean of the bike. On a motorbike, it also allows the rider to gauge the angle of lean. At motorbike speeds, it also generates a slight turning moment.
I find it faster on a bicycle to press the inside knee into the top tube and drop the upper body into the turn. With no power to the rear wheel, there's nothing there to overcome the wind resistance of the dropped knee and motorbike technique is not really appropriate.