they are stacked, and every video I've referenced shows them using jumpers which made the declaration in the code for the connection is easier to define I don't know if there is a difference with them being stacked. The reason why I chose software serial because using hardware serial you have to use TX 14 RX 15 TX 16 RX 17 TX 18 RX 19 for the additional serial usage. but the boards aren't connected to those.
