The first step to change is admitting this.
Your boundaries are your values. Boundaries are representative of how much or little you respect yourself.
You must make your boundaries about you.
Once you get clear about what matters most to you, then you can take the bigger step of communicating that to the others.
You are not responsible for what they say, their reactions or for the daily choices they make.
Since you can't change other people, change how you deal with them. They may be motivated to change if their old ways no longer work.
The best way to figure out your own boundaries and consequences when people cross them is by sitting quietly down with yourself and making this all about you.
Keep in mind: boundaries are about honoring your needs, not about judging other people's choices.
You present your boundaries clearly to people and then let your behavior do the talking.
People WILL test, push and disrespect your limits. You'll know you're getting healthier when this doesn't get an emotional reaction out of you.
The biggest part of setting boundaries is HOW clearly you communicate them.
You can have the most healthy set of boundaries on the planet but if you do not communicate them clearly, you are going to create some really confusing relationships, both for you and everyone else involved.