TLDR - can i provide advice to my abusive parents if they ask for it and what options other than my sister moving out are there that can be pursued considering boundaries while she's living at parents home isn't respected?

I (23m) am a family of 4 (20f, 56m & 58f). When I was 13 my parents were judged and abused by both sides of my parents families resulting in both parents and children having all ties to extended family cut.

Due this; as any human would, didn't know how to handle it and became verbally, physically and emotionally abusive towards me. Now I can't deny they gave me every opportunity they could BUT when something didn't go the way my mother wanted, or it wasn't done PERFECTLY, the physical, emotional and and verbal abuse began. Then at 21, they kicked me out, but continued to stalk me on the way home from work, even attempted kidnapping at 10pm at night for the following 6 months.

Over the following 2 years and 1 month, I've spoken to them both in person and over the phone exactly 10 times, and while I'm not angry anymore, they are still repeating the same saga with my sister.

My sister moved out of home early 2022 and moved back in 6 months later, only to then apparently treat my parents in "contempt". They have since come to me asking for advice as to what to do. I've advised, that while she's living in their home, they're well within their right to have boundaries in which my sister needs to follow eg. Do her own laundry, cook her own vegan meals, let them know whether she'll be home that evening and pay back the $16k loan that she demanded to buy herself a new secondhand car. Now none of this happens and I've since advised that the best option for my sister provided that she's willing, is for her to look for a small apartment or unit so that she can live her life, her way.

1. Is it my place to provide advice even if they've asked for it

2. What else could I suggest to all parties involved to help amend the family to some degree