Our extended family have never lived close by. But, I can guarantee, they would not have interfered or been involved in any way in the discipline of our children.
Extended family has no business weighing in on one's child raising skills unless there is some kind of abuse-then everyone should step in.
BleuBrenda, you need to draw very strong boundaries and let them know that you will not tolerate certain things. It isn't important that they are trying to help--if a man is drowning and someone is trying to help him, but keeps dunking his head under in an attempt to help--it is not help at all and the motives are unimportant.
I would tell them, I love you, but you are out of line and this is my son, and I am the parent and will make the decisions I need to--I will ask for help when I need it.. It is an entirely different matter if you ask them for help. Good luck!