Microcontroller Wired-OR connection
You have basically configured an I2C bus of sorts with each device on the bus pulling the line low as required.  I wouldn't be too concerned about current moving between multiple low pins as it will likely be in the order of milli to micro volts but if you are concerned you can always add series resistors on each PA1 pin before connecting to the output bus line.

If the output is just for detection by a separate high impedance input device then you can even raise the 10K pullup value to save on power draw.