Semi-Affair.. ...........?

i have two older brothers. One of them is getting married in a little over a year. The woman he is going to marry is a total skank.. I think she maybe trying to start something with my other brother. The other day we all went to lunch, and she wore a very low cut blouse with extremly short shorts and high heels.. she looked like a hooker. I think she may also have another boyfriend, besides my two brothers. I really think this situation could ruin our whole family life.. what should i do?