I am so sorry to hear of your stressful situation. It is unfortunate that you do not have the support of her family and my first thoughts are that you need to protect both of your children from possible harm through legal resources. Can you share what part of the world you are located in...it would help others in sharing what they know about the legal system in your area. I have a lot of knowledge about Florida law, some knowledge of other states and very little about other countries.
In Florida you could actually file a petition and see a judge and get her court ordered into a treatment facility... with the unborn child, her hospital visit and your testimony with most judges it could happen. It is called the Marchman Act. Your state/country? may have something similar.
Well coordinated interventions by loved ones can be successful but it is infinately more helpful if you have all family members working together. I think the best book on this subject is No More Letting Go by Debra Jay.
Have you thought about a weekend AA retreat? It is a sober event and they can be inspiring, educational and life changing. If you can find one in a short enough time and make arrangements it might be worth considering.
AA meetings in your area are another resource. There may be other alternatives as well including counseling with an addictions counselor.
Have you been to an Alanon meeting? This might be a real help for you and regulars could probably give you lots of advice on area resources that might be helpful.
You might want to consult a lawyer... usually they will consult for free (make sure when you call) as they may have better knews about yoru chances of getting temporary custody than you think right now.
You will find a lot of support and wisdom on this website... welcome.