I think i have a ghost in my house, he seems harmless..but could he turn out dangerous?

okay, so my family has lived in this house for 12 years now..and there was a old couple that lived their before us, the old man died and the wife moved so we bought the house. I have been moved out of their a year, and just moved back there. my sister, boyfriend and i live there alone its a 6 bedroom house so it huge. weve been noticing things...my sister has seen a persons head move in the master bedrooms bathroom window one night when she pulled in one night late. she refuses to talk about it. then i was in the shower, and i heard a loud enough knock on the door to where i called my bf, he was in our room with the dog watchin tv, he swares up and down it wasnt him, i know somebody knocked that door, then the security thing on the window fell off when i went back in the bathroom...is the spirit messin with me or what?? we see shadows at night moving...the stares seem like someones walking on them, we hear somebody at our door at night sometimes...and our big black dog was staring at the hallway that goes straight up stares..she was barking and going nuts as if something was there..something shut the door when i was cooking one day, i left it open and all of a sudden the slide glass door jus slam shut so i walked in the den and our dog was jus looking up at me as if she didnt hear it or anything..we hear whispers and the cats even cry alot outside around the house...we are deff at the point of moving out, could he turn out dangerous?? or is he just living with us minding his own business?? or is their even a ghost?? we all belive in ghosts now, our house is quite and we feel like theirs a spirit no doubt. He hasnt hurt us or thrown **** or anything, but we just dont know. we wont mess with those wigi bored things..those just dont seem safe to use, im a christian and think they open portals to other deminsions. were scared well make him mad bringing a professional over to the house. WHAT do we do!!!?? please help