Feel free to lift twice a day however you need to do a program that is incorporating the fact that you are doing twice a day sessions.
Pop over to
www.t-nation.com and find chad waterburys high frequency training and that article will show you how to do it by incorporating recovery techniques.
The workouts are great too and with that extra activity you will be able to lose weight nicely. Just don't cut calories too low as you need lots of fuel to train this way.