I suspect Sarah’s parents know exactly how shit a mum she is and do what they can to support those kids but reality is that they have done their time. It’s not a grandparents job to parent their grandchildren. My parents are amazing and do offer to help out and are around for my kids but it’s not on them to be my childcare, my surrogate parent, or to step in and parent for me. Sarah chose to have those kids, she should be parenting them. She could. She just chooses to do the bare minimum so social media tells her she’s amazing. She isn’t disabled, she isn’t an addict, she doesn’t have mental health issues that would mean she isn’t able to function for herself let alone her kids, she has a spouse, a house, a job, they aren’t living in poverty, she just chooses not to parent properly. Her parents could step in but they are elderly and maybe don’t want to or can’t.
Reality is they have enabled her and spoiled her and pandered to her. Her eating issues and how unwell she was probably has them terrified to say anything because they know she’s not that far off being unstable so they do what they can, but really it isn’t on them.