Codependency Support Group
Codependency is defined as someone who exhibits too much, and often inappropriate, caring for another person's struggles. A codependent person may try to change, or feel shame about their most private thoughts and feelings if they conflict with the other person's struggles. If you are on a journey towards self-love, this support group is for you. Join us and find others...
My own understanding is that boundaries are fun and interesting, so I find a boundary to be rather easy to decide, but that is only true now because in my younger days I had no boundaries and or dysfunctional boundaries.
This link here is a little long but I like it about boundaries:
https://independentfew.wordpress.com/2015/02/03/boundaries-walls-and-denial/
Most likely (I guess) the reason you are having a hard time deciding is because you are thinking too far ahead, as in thinking of however to enforce the boundary? and what happens if the other people violate the boundaries? and that kind of thinking can drive a person crazy instead of enjoying the process.
A book about healthy boundaries based on Christian principles is here:
http://www.amazon.com/Boundaries-When-Take-Control-Your/dp/0310247454
And this book is free to see at the Libraries.
Peace.
Then I started therapy, reading books and working on myself. I've made a lot of progress with setting boundaries and feeling comfortable with boundaries, more so than I used to be. I used to not really understand boundaries, but once you learn about them, work on yourself and use/stick with these boundaries, you get more comfortable to the point where it's a natural thing in your life.
Check out the Boundaries/Boundaries workbook. They go hand in hand, and the workbook really gets you thinking about where you need to set boundaries. It taught me a lot and I think you would benefit from it too. :)