First, realize that you are an emotional vampire. After you realize that, the next step is identifying any patterns behind what you do. Are there particular people you are more of an emotional vampire with than others? Are there times of the year that you are more of an EV than others?
If there are patterns, take steps to change them.
When you are doing EV things, identify, what it is that you really need. When you are doing it to a family member, what is it that you are really needing? Rather than suck the life out of them, identify if you need love, attention, affirmation, support, etc. Give yourself permission to ask for those needs rather than take.
Simple things like asking rather than taking go a long way.
These will give you a place to start and plenty to work on. My book which is now on Amazon talks about how I dealt with the whole matter, through both what worked and what did not.