Question regarding the film poster & ending *possible spoilers ahead*

Got a question all...

I've just seen this film and have some questions. When researching this film before watching, the original film poster shows a group of people with no eyes. I presume those were the underground dwellers. Yet, when the film takes us into the lair where they live, its only two of them. Since his companion died early in the film, he was alone for awhile until he kidnapped the woman. As we see the finale, we see that long dark corridor, we only hear the voice of the man. Are we to presume there could be more of them or was he the last of his kind? Do you think he had not died and killed the cop?

Any ideas, opinions, or thoughts?