Family discussions are a great way to resolve family conflicts. Such discussions work best when they're not bitch sessions where everyone blames each other for the problems in the home but rather discussions in which one problem is addressed at a time.
Third, and I cannot stress this enough: Join a support group where you'll find camaraderie and ongoing help from people who have already faced the issues you're struggling with. Although counseling is usually the first thing suggested (and I also suggest it to you now), the importance of close friendships when facing something like this is often overlooked. Consider visiting the Stepfamily Expert message board here at iVillage for great virtual support. If you prefer face-to-face support, visit Bonusfamilies.com for information on joining a group or even starting one in your area.
Finally, reach out to the bio mom. She's probably very frustrated right now, but as time goes on, she, like Dad, may be faced with the guilt associated with not living with her son. If you can help to bridge that gap by improving communication and easing stress, all will be indebted to you. You'll be the leader your family needs, and you'll quickly see your frustration lessen as your family begins to flourish!