My brother just got engaged and i think he's making a HUGE mistake! What do i do???

First of all...I didn't like his fiancee even before they started dating. She was rude and condescending... and and and she doesn't even have her legal citizenship papers!!! Do you know how HARD it is as an american citizen to marry someone who is in the U.S. illegally!!! Both of my sister's married illegal aliens and they are living a nightmare. My brother is an educated college graduate and his fiancee can't even speak english! Gawsh! It stresses me out! How can i not make it MY problem?