In the first bar the weights are of volumes proportional to their respective weights. When they are lowered into the water, the forces acting on the arms of the bar will be altered (according to Archimedes' principle) by amounts which are proportional to their volumes. Therefore the relative change of forces acting on the bar will be the same for both ends. Consequently equilibrium will not be destroyed underwater.
On the second bar, both weights will 'lose weight' under water by the same amount and since their weights are different, the relative 'loss of weight' will be greater for the one which weighs less. The ratio between the forces acting on the arms of the bar will alter and equilibrium will be broken. The end of the bar at which the relative loss of weight is less will tilt downwards, i.e, the end with the 3 kg weight.
2. Generally speaking, no, since at every point on the earth's surface there is a magnetic inclination (the lines of force of the earth's magnetic field are not horizontal).