Simultanues closing

I am looking at REO’s to flip. I was told that I couldn’t do assignments, but it was suggested that I do a simultanuous (mispell) closing. I know there’s some risk with doing this, that’s why I will only do it with one of the “I buy Houses” investors. Are there any legal issues in some states regarding this? Is this a common procedure with other investors? Finally could someone tell me step by step the process for it. I would like to look into doing this.