One of the difficult things about setting boundaries with others, whether we are new to the practice or well-versed, is the worry we are hurting someone else or being too harsh. Are our expectations unrealistic? Are we laying down the law with too heavy a hand? But even if we are, don't we deserve respect and safety too?
The thing about setting boundaries is it isn't about what the other person thinks about them. It's about what we think about them. If we feel they are fair, we will explain it to the recipient in a way that seems fair and reasonable.
When setting boundaries, it's important to focus on YOU first. What do YOU need? What do you need OUTSIDE of the context of what you think another needs, or what their feelings may or may not be?
Boundaries are often an individual thing, and so it should be treated as an individual decision.
We all must learn rules. We all have been learning rules and consequences our whole lives. So understand that if you feel your boundaries are fair, it is ok to set them. The other party will come to understand, will come to adjust and acclimate. Just as they (and all of us) have done, constantly acclimating to new and changing rules.
They will come around. When is up to them and not of your concern. Just because boundaries have been set, doesn't mean they can't be adjusted later if it makes sense. But give these boundaries, yourself, and the other parties, time to try them out and see how they sit before you change them.
This mentality can help you stick to your boundaries. If you know they don't HAVE to be permanent, that you can change them at any time, then you will stress less about the impact of them. You will try them out an stick to them for a little bit, because you know there is always the freedom and option to change them back.