What could be wrong? Frightening behavior in a toddler

There is a 3 & 1/2 yr old cousin in our family who has been kicked out 2 preschools for biting and hitting, exhibits odd behavior i.e. hitting and biting parents and other kids, pets (tried to kill a new pet, new pet was removed from home) in the family, pees on the floor, refuses to poop in the potty, speaks in a very high almost falsetto voice 70% of the time, throws tantrums...sadly the list goes on.  But this Christmas was the pinnacle for odd behavior, he poured hot coffee down the back of one of the children, blackened another’s eye, peed all over the bathroom floor, and became very upset with his father proceeded to the kitchen to look through the kitchen drawers, when told to stop said "I am very mad, I need a knife, I want to cut him” I am not kidding even slightly this is exactly what he said.  Everyone in the room was shocked and froze but no body did or said anything about it.  He was not allowed the knife...but his parent’s grandparents and great grandparents will not acknowledge there is an issue.  My spouse and I have tried to approach the subject but are told he is just a bit of a bully and he will out grow it.

Well...to some degree this is not our problem but they will be delivering a new baby in a month and we are worried.  
This isn't normal behavior...Is it?

[tiredbuthappy]

absolutely NOT normal behavior. either they are in denial, or coping with it privately and choosing not to share with the rest of the family. unfortunately, as a cousin, there is not much you can do other than protect your children by refusing to let them near him.