Why are my cats acting different?

I have 2 outside cats, smokey (who is very shy and never talks or makes contact) and Pingpong (who is more brave and loves to be around people) they are both brothers and tonight as i was laying down by my window, smoky comes up to the window and meows forever! and it isn't really a warming meow, its more of a terrifide voice. this is very unusual for smokey to even come up to me. pingpong later shows up and bites him "i think to calm him down" and then they both start staring into the darkness and they keep doing that think with there ears to show there scared. Im really worried because my mom thinks this house is haunted and i wonder if my cats are seeing something im not.