I am trying to use 2 2x12s as a header put a 4x4 at each end 16ft will I be OK its an over hang on the house about 5.5 feet wide and 16 ft long

You don't provide enough information to answer the question.

We need to know at what floor level this header will be (In other words, how many floors will be above it)...

Whether it is located in or will be part of an exterior or interior bearing wall or beam...

Whether it will be used to support ceiling joist and roof loads...

What your local snow loads would be and a host of other things.

Generally speaking, the maximum span of 2 2x12s under most conditions would only be slightly over 8 feet and any 16ft span would require an engineered header, steel, or a truss.