It is known that a member of our family watches inappropriate things infront of their child. (Trying to be as vague and non identifying as poss) When i say inappropriate i mean the child is not quite 5 and things like the walking dead, south park,family guy etc , me and dh find this concerning we have dcs ourselves and would never do it. You wait until they are asleep a sometimes irritating but important part of parenting the bizarre bit is this persons parents , partner (dn mother) and brother all live on the same block , see each other a lot must see/hear far worse than we do but then do absolutely nothing 
will not say a word against it.there are pre existing issues with DN swearing with the same response given. The other night we were there and as we were leaving he was about to stick a 15 rated horror on at about 8pm DN still milling about awake due to gathering. My DH quickly said "arent you putting her to bed then?" He looked bemused and said no she was fine. My DH basically said are you serious youre going to fuck her up big time, granted not great language infront of kids but i think the sheer disbelief and the point was valid. No one else in the room said a word though and when a few other horror films were mentioned his mother said "stop messing about now" which as were not there a lot makes us wonder if its a wierd joke at our expense, any advice how to deal with this situation whilst safeguarding our own children.