Should be as simple as eight resistors for the LEDs and eight diodes for the bell. How to connect them depends on if the 12V is high-side switched or low-side switched. If it's high-side, i.e., one output is "ground" and the other is either 0V or +12V, then use 8X 1K resistors, one from each output to the anode of a LED, and ground the LED cathodes. Use 8X 1N400x diodes, with the anodes each to one output (along with its LED resistor), and all of the cathodes connected to the relay coil, and the other side of the relay coil grounded.
If they're low-side switched, i.e., there's a constant 12V, and the outputs go from floating (or maybe a 12V pullup) to a switch to ground (e.g., a transistor collector), then connect all 8 LED resistors (on the anode side) to the +12v, and each LED cathode to one of the outputs, and the 8 diodes' cathodes to the outputs, their anodes together to the relay coil, and the other side of the relay coil to +12.
Good Luck! Rich