Estranged grandparents

We have been estranged from our granddaughter and our son for 8 months and it feels unbearable. It’s like we are going through bereavement over the loss and are finding it difficult to move past it. My husband says he doesn’t want to get over it or move past it because he fears it’s “forgetting” our beautiful granddaughter. We had her in our home 5 days a week and provided structure and consistency for her which she wasn’t receiving at home. She was often filthy, hungry, and overtired from being up all night. They moved across the country and we visited monthly and checked in online almost daily. We had concerns of neglect and bought a home there to be closer to them to offer support. After moving there we were told there was neglect and domestic violence in the home. I told my DIL she had to remove her daughter from the home and we found help her any way we could. She took up and left the state back to our original area with our granddaughter. She then cut all contact and filed a restraining order ( which did not get approved in court.) We believe she is back with our son. My intervention was for nothing, they are most likely in the same situation with no advocacy. We are beyond heartbroken and feel like we can’t even function some days.
How do we heal from this? How can we repair this? My son won’t respond to any attempts to contact. I feel so desperate, helpless and hopeless. Any advice is greatly appreciated.