Answer:
What stays the same size no matter how much they weight?
Often held but never touched. Always wet but never rusts. Often bits but seldom bit. To use it well you must have wit.
When I live I cry, If you don't kill me I'll die.
I look at you, you look at me, I raise my right, you raise your left.
There is an ancient invention. Still used in some parts of the world today. That allows people to see through walls.
I am your mother's brother's only brother in law. Who am I?