You can't just use a single crystal and wire the clock signals parallel, but you can use an external clock generator and use the same clock for both circuits.

For the reset, use a reset circuit rather than a simple RC. If you buffer the reset output, you can use them for both devices.

If you need a watchdog, you can use a monitor / watchdog / reset circuit on one controller and add some code to have it operate as a watchdog for the second controller. The reset of this one can then be controlled from the first controller.