Hi cbusmom:I'm sorry that your son has BPD and that the 2nd one likely has it as well. I can understand how frustrating it must be and upon reflection, that you feel that you contributed to their condition.
I have been reading on the web and stumbled across a page VeryWellMind.com. I found an article on there "Emotional Invalidation During Childhood May Cause BPD" that has some very interesting info in it.
After reading it and mulling it over I mentioned to my H that I think we might have played a part in causing this in usBPD27 and dsBPD22. I read him some of the info. In the article it mentions a predisposition for strong emotions... Ding Ding Ding. And guess where they get it from? Me! So in the conversation with H I start getting emotional and tearing up and he IMMEDIATELY tries to shut me down with phrases such as don't go getting all upset' or 'there's no need to act like that' or 'I had a stepdad that made me man up and I didnt grow up to scream and yell at people'. My first response was to feel shame for my over emotional actions. Before I would have agreed with him and tried to pull myself together or went somewhere and had a little private cry. Not today though! Because of the article I was able to tell him calmly that I my emotions are not something that I should be ashamed of and that THESE statements are EXACTLY what the article is talking about.
Don't be too hard on yourself. Genetics deals the hand (from both you & your son's fathers) & the predisposition is there for various mental health issues. Some mental health issues will evolve even without an invalidating environment & there can be a need for meds to help manage them. Sometimes, mental illness can skip a generation & when you go back a generation or two, many mental health problems weren't diagnosed but people would talk about crazy uncle Joe or difficult Aunt Sue.
What tends to exacerbate things is when someone lacks the skills to manage distressful situations and/or their emotions. Have your sons had any DBT therapy? DBT skills can be beneficial for anyone. Perhaps it could be beneficial for you to give it a try for yourself. If formal therapy isn't possible, there are workbooks you can buy & some online opportunities. Marsha Linehan is the best author for DBT books. There are a lot of skills here in the Workshop Section that can help anyone.
We can all benefit from practicing mindfulness skills and learn ways to manage emotions like anger & sadness. Emotional Intelligence is something that helps us do better in all aspects of life - to handle emotions and to communicate more effectively with others.