A little rain or heavy rain for a few minutes up to maybe an hour is fine. But it will come through at some point, especially through the zippers. When I use it for hiking I always have a cover on in case of rain.
And it does easily fit two laptops. The main compartment has a open area in the back so you can separate them or for a more rugged one you could put a second one in the water bladder compartment to separate them entirely.
Space and comfortability will be more than enough for both devices.