Dude, you've got to stop drinking. You're completely letting MIL push your buttons. You need to have your head clear.
You need some alone time with your wife and let her know that you still love her. And you need to remind her that you're her husband and "the man". I'm afraid that with MIL there in both of your faces, your wife is losing confidence in you. The old bitch seems to act like suddenly she's the queen of the castle and able to order you around like a toy poodle.
Go through the WT lib CD and find some stuff that tells the parents to butt out of their children's lives and marriages. There's some stuff in the Family book and other farticles showing how parents can interfere and wreck their kid's marriages. Interrupt MIL with each individual quote. Remind her that she's not a man and that according to Watchtower, she needs to find a husband to tell her what to do. Maybe share some of the priceless JW quotes that insulting refer to women as emotional and unreasonable. Remind her that you're a man, a reasonable leader, and she's a confused, emotional woman that needs a headcovering. Maybe that's taking it too far...
But it might be worth mentioning to her that of course you and your wife are stressed out. You've had a messy house 'guest' that's overstayed her welcome and you haven't been able to have a date night followed by loud, passionate sex for over 2 weeks!