There's a reason that offices like CPS have anonymous tip lines... so that when abuse/neglect is seen it can be reported without the fear of retribution for the one who had the nerve and the HEART to do something about a bad situation.
Call it in. If you're concerned about family harmony then use a payphone. Say you visited a friend next door and it was awful... perhaps your 'friend' complained of it to you but said they didn't want to cause a storm... so you took the liberty of reporting the stench and horrible conditions for them. That way if the 'agent' who takes the call does slip and tell anything all it will point to is a 'friend' of someone in the area... not directly at you...
Bit more complicated that way, and they may not even bother checking since some ignore such calls and only respond to actual complaints filed and signed by neighbors... *shrug*