If two boys jump and two boys jump, 'two boys each (=four boys) jump' makes sense?
"Two boys each jump" means that two boys jump, not four. This phrase means the same thing as "Two boys jump", with the word "each" emphasizing that each of the two boys jumps.
This is a different use of "each" than it seems you were hoping for. If you wanted to talk about multiple groups of two, you could say something like "Each two boys jump". This is a very awkward way to phrase it, and it would be much clearer to say "Each pair of boys jumps".
Note that nothing in the word "each" indicates that there are two things being referred to—there could be three, fifty, any number.