Photo prints made back then were processed in liquid chemicals. You COULD soak the whole lot and then they would come off the board. However...CAUTION. Once wet the emulsion is very fragile and would scratch easily so minimize getting your fingers on the picture area. You could actually scratch off the emulsion.
TO dry them a hairdryer on a med temp and wind speed would work to dry them... of course if you could actually find the negatives [those funny orangish strips] you could just get new prints made from them and the color would be much better then what you have now!