Thank you for sharing your experience, as unfortunate as it is.
I believe you were responding to the following in my article: "Family support (if that’s available)."
To be clear, there's a huge difference between getting family support in an emergency and your unfortunate situation with your sister and her husband, who elected to impose on you without asking in advance if you'd be ok with it, mooching as you call it.
I suspect that your reaction would have been far different had the situation been that your sister had lost her home through no fault of her own, and asked you if she could stay with you until she's back on her financial feet.