How to find out if a bequest if signatures are authentic?

My brother passed away in Oct. 2012 and his girlfriend forged her name on all his property. Our family has been trying to track down the people that signed the bequest, to see if itis legal. We've only been able to speak to one person who signed the bequest, but she states she didn't remember much. We believe it's fake because her and her sister who works for a Judge wrote it up, after there was already one.