Micro controller serial communication question
You can't, in general, connect them to a single serial port. You'll need a microcontroller with (at least) two serial ports.

Sometimes, if you're trying to really minimise the cost of the microcontroller, you can implement a seral port using GPIO pins and I/O instructions. This can be very effective for a transmit-only serial port. But I would not recommend it for a project like this.