Driving an H-Bridge from one pin
Q1 and Q3 are set up in a correct half bridge configuration. Q4 and Q2 are not because this configuration is conducive to shoot through. Q4 can source current out of the base and Q2 will sink it through its base. This will cause both Q4 and Q2 to be on at the same time. Also there would be no way to hold the setup completely off. You need at least 2 pins to drive a full H bridge.