Hi
1.Whilst and while it's the same word.No difference between them. 2."In vain" means for nothing.So in other words it's "my brothers will not have died for nothing". 3.Well,couple means two,therefore "couple of" means two of.But nowadays "couple of" can also mean more than two of because people aren't using the term accurately.So when I say for example that I want you to buy me a couple of thing that doesn't necessarily mean that I want you to get me only two things.It can mean that I want three or four things.So to sum it up,"couple of" originally means two of,but you can also use it when you want more than two of,because no one uses the term correctly anyway...
