One sub is definitely damaged. You can say the spider is still attached, but you posted a pic clearly showing the spider detached from the cone. It might still be attached part way around the spider, but that just means the spider will work against keeping excursion linear, the opposite of its intended purpose. Not trying to sound like a dick, just wanting to make sure you fully understand the situation. The one sub is definitely bad.
If one sub is rated at 400 watts, and the other at 800 watts, they are almost certainly very different subs and should not be attempted to couple together. The person you bought these speakers from doesn't seem to know much, Id avoid his advice in the future.