Let me first say, thank you for analyzing this.
I literally felt sick to my stomach reading your analysis because you are so on point with it. I was almost wishing I was wrong to even think this to be true but it is.
But what's so frustrating is that my mother is goig along with it and its messing up my relationship with her as well.
I am really telling you the truth when I say that I go out of my way to avoid any drama with anyone. I like peace. I do get feisty when confronted but that's because I get annoyed when people start stuff with me for no reason and my sister does just that.
I wonder if its the 6th ruler (Venus) is in my first house (Taurus). I've heard that that brings conflict to me with women without me looking for it.
no offense to the analysis, but it's not that unlikely that you would have had a row with your sister (or anyone for that matter) and for someone to be internally angry if they are externally angry. Internally angry is not secretly envious. I don't know if it's anger, I don't know what the content of what she is saying is, and I'm always skeptical on motivations put on another's actions as we can't know the veracity of these interpretations. for example, when you say your sister reacts for "no reason" you simply are saying that the reason is not clear to you. my point is, I don't know if you can say you suddenly know for sure now that your suspicions are correct.
For facts, as you've stated them, we have 1) your sister has a failed relationship 2) has a child from that relationship 3) had an outburst in the way of someone upset around the time your son was born 4) tried to harm herself shortly afterward. She 5) talks to your husband about you - we don't know what the content or intention of this is and 6) you think she pushes your children away from her (emotionally?). We also heard that 7) you have had family discussions with her but you feel she is not stopping behavior that causes "the" discord - was that clearly iterated to her? Is it something that can be stopped? and 8) you are "feisty" when you are confronted but excuse that because it's for "no reason". again, you don't know what that reason is but it does not mean that there is no reason.
My surface interpretation is that you guys need a mediator or time apart** - it seems like if you have family discussions (several) and are around each other a lot you may live together or spend too much time together. From the chart I also will add onto what was stated before - she is in your 7th house not connecting with you, and currently (the moon) looks like it is stressful events for you and will square her - but not now. Her 5th house ruler (her son?) is retrograding toward her - did her son move away from her and now may be reconciling? and you are in her 6th house, in her day to day life? You are strong and if you read the reception of her Mars liking Capricorn - your sign (I believe people said mars is exalted in cap) or not being averse (not in detriment or fall in cap) does not show her having ill feelings toward you, however perhaps saturn (you) being in detriment in Leo (her sign) means you don't accept her. Again I am still confused as to what i think is being said is "correct" in terms of reception reading.
**I think your sister in particular, may need you to speak up, you said you avoid drama that is "for no reason", but she may need you to speak with her about what you see as drama. So, if the communication with her, and your mom isn't working, you may need something else.
Her being upset with things in her life, she may feel pressure cooked in an environment that surrounds too tightly or doesn't release tension by communicating effectively (and of course, anyone else in that environment like you). Of course, if she feels pressure cooked it doesn't mean she gets to blame you, but it could explain irritability, sensitivity and outbursts when things around her relationship is brought to attention.
Also your fifth ruler left conjunction with her - your son? did anything happen before your sister seemed to avoid your son?
Venus is your mom ? (ruler of 4th), and isn't in detriment of either you or your sister's signs, which might show neutrality (not taking a side) - but there are stressful events (square with moon).
I hope you can figure out a situation to truly diffuse any drama.