The honeymoon is over- help!

My husband and I have been raising our newly placed pre-adoptive kids for two months now- our son (age 11) and a daughter (age 10). They are our only children. Our daughter came with more psychiatric diagnoses that you can count on one hand; She had no honeymoon period at all, and had tantrums for 2-3 weeks at home and school nearly daily. With firm, clear and consistent boundaries, she is now off of all medications and doing excellent in school and at home. Before we brought our son home, we were told by his foster mom, teachers, attorney, case manager (and everyone else who had ever met him), what a sweet little joy he is and how well behaved, etc. We noticed this "perfect" behavior was perfectly very fake, and even cheesy. For example, when redirected for something such as leaving his belongings on the floor of the kitchen, he would pause, then very, very sweet say, "Okay, Mama, I'll just go pick them up!!!!". After a month of this "perfect behavior" he would decline after a few days and erupt into a very frustrated and angry mood, slamming doors, throwing chairs, etc. Over the past few weeks, his "bad days" have become more frequent than the fake "perfect" days, which we have been viewing as progress. We would rather him be himself than act perfect and be fake, we just want him to learn to manage emotions appropriately. However, the past 3 days he has been very violent toward me: he has kicked me purposefully in the stomach four times, and on one occasion, tried repeatedly to bite me. Upon dicussing this behavior with him, we know it was learned from his father who battered the children and their mother. He even admitted to my husband that he targets me (and not my husband) because he feels that I can't hurt him back. Upon hearing this, we explained to him that both of us are stronger than he is and although we have the ability to hurt him, we make the choice not to do so, and that he should also make the choice not to hurt others- since that conversation he has been targeting his sister and kids at school: He has hit/pinched/kicked/thrown things at kids at school and his sister. We are desperately trying to get him into therapy and into see a psychiatrist, but no one can get us in for another month. My husband and I are 100% committed to these kids and, despite our son's violence, we will not disrupt the adoption. One thing we have been doing is sending him to his room (we had to take the door off because he was barracading himself in his room and repeatedly locking the door), and he will stay in there, most of the time. However, when given the chance, he continues to use violence against anyone he views as weaker than himself. We've been doing the heart-to-hearts and exploring the options, even providing him with healthy ways of expressing his anger... Does anyone have any similar situations or advice?????