Hi there helpforsis.
I don't want to feel like the bad guy, I just want peace.
Peace is a good goal. If you are hoping for peace, as in no conflict, no dysregulations, etc from your sister by avoiding telling her things directly, I don't think it is going to work very well. That is what you have been doing and it has not worked has it? If you want things to change, you have to stop doing what has not been working.
First, if your mother chooses to try to pass gifts along to you, I would tell her that you have told your sister you do not want gifts and that she (your mother) needs to return the gifts to your sister. Your mother is allowing herself to be pulled into your sister's drama and as a result is dragging you along with her. If your mother accepted the gifts, it is her responsibility to give them back.
Second, when your sister mails your kids gifts, send them back or refuse delivery. You might want to remind her that you told her there were to be no gifts, but only remind her once. Your sending the gifts back will be a reminder.
Now, are the above strategies going to keep peace? Nope. Not right away at least. If you are consistent on sending the gifts back and consistent on keeping your boundaries and refusing to be dragged into the drama things may change with both your sister and your mother. Boundaries.
Often times people will say they tried boundaries and they do not work. Often it is because they were not consistently applied. Being consistent is vital.
Another thing to remember about boundaries is that often the pwBPD will amp up their behaviors, yell, rage, cause problems etc. Stand firm. things will often get worse before they get better, but they do get better. Even if your sister continues to send gifts, **you** will get to the point where this behavior is not so upsetting. Empower yourself. Say no. Avoiding her getting upset is not possible. Expect her to get upset. Expect your mother to try to push you to accept gifts. anytime we change the way we interact within the system, there will be upset and chaos at first. Keep at it. It took me about a year and a half to get my mother to stop yelling at me and putting me down and trying to touch me. I had to hang up, walk out, repeat myself over and over. My brother and father used to plead with me to just make peace with her. But making peace with her required me to accept things that were no longer acceptable.
It may take time, but peace for yourself is possible. So many times we try to twist ourselves all around in an effort to avoid causing problems but by doing so, we betray ourselves and we keep going round and round in the same circle while walking on eggshells... .and those little suckers hurt.
Your children are *your* children and you have the right and obligation to determine who will and will not interact with them in any way.
Helpforsis, none of this is easy. It is hard to change decades of behavior, and I am talking about *your* behavior. You probably will be nervous, anxious, exhausted. That is all normal when changing how you interact with your family. So if you feel those things, tell yourself it is expected, normal and usually means that you are doing very well at breaking old patterns.
Do not expect your sister to just accept your boundary or to listen to you. She is not capable of doing so. Change things up at your end.