spirit, this type of situation is so hard to deal with. Our heart wants to believe and trust another, or at least to not hurt them, and yet we've already experienced so much hurt in these relationships.
In the beginning, it helped me to remind myself over and over and over of why the need for boundaries and eventually VLC became necessary in the first place. There had already been so many opportunities given to my ILs, so many chances, so much explanation. I had to harden my heart and remind myself that the time for turning back was over, and now was the time to calmly, kindly (it was my goal, rarely achieved) hold the boundaries.
It also became helpful for me to realize that staying steady and consistent was a genuine gift to someone who has a chaotic inner and outer world. Like with small children, I came to believe it was genuinely kinder to become very consistent and predictable rather than changing my mind and behavior when the hoovering would begin.
It's hard, and we all have our own stories and circumstances, but know that you are heard here and not alone.