Your 妯娌 is same as my 妯娌 --- always pretends doing good to me in front of 9962.
To me, I decide to give up, because in my case no matter what I say what I do, my 9962 still think I'm wrong & I'm bad. Every things done by 妯娌 is good, even she lies and says black words behind 9962's back.
I understand your relationship tension and pressure. To me, they are not worth my efforts, so I withdraw and disregard them altogether. I would rather want my happy life myself and with my own family.
If your 9962 treat you good, may be you can compete with your 妯娌 because it's 妯娌 who stirs up all troubles. But if your 9962 are not good to you (like mine), then it's not worth. Every time just stand besides to watch their 'movies'.