If my cousin marries, what would her spouses siblings be to me
They would be your second cousins in the US and first cousins once removed in Europe. However, most people find it easier to call them nieces and nephews. You can go to http://en.wikipedia.org/wiki/File:European_kinship_system_en.svg and http://en.wikipedia.org/wiki/Cousin for more information.
They wouldn't be any relation at all; but in our family we fondly call them "cuz".