OK accepting that they're square taper, then your Schwinn would have a threaded 1.370 x 24tpi BSC, (now ISO) BB. The main variable would b spindle length, but you can measure that anytime once the cranks are off.

Removing the crank requires a crank remover, but be careful, they come in 2 basic types, the older version for square taper, and the more recent version for OS splined spindles. The difference is in the pusher pad, and you need the right type.

Once the cranks are off, you can work on the bottom bracket, which requires different tools according to construction.