How should a family manage an estranged relationship?

Siblings etc often don't have chance to "pick a side" but will also be cut off.
We are currently estranged from OH's sister. Our children understand and support our decision but keep in touch with her and we respect their decision .
A friend is on the verge of being estranged from her daughter. Friend is desperate to do anything to keep the relationship going, but her OH is so hurt and angry about how they have been treated that he wants to break contact. Their's was a rock solid marriage but is now under strain

Often when there's an estrangement, the entire side of the family is also estranged.

In our case, as far as we are aware our ES remains in intermittent contact with his brother and we think him living in Aus. may well have something to do with it.

ES also had intermittent contact with his paternal GM but completely cut my mother out of his and her only GGC's lives.

As for whether one parent should walk away from the AC whose estranged the other parent, that's a decision that only they can make together but I do wonder if that is the case, how sustainable that can be long term.

Mr. S. and I have kept one another going for the last 13.5 years and neither of us thinks we could have coped without that. One of us remaining in contact was never an option but if it had been, we come as a pair as united we stand and I'm certain that divided we'd have fallen.

Adults should manage their own feelings without needing others to choose sides. Unless objective abuse is involved, I would view the person demanding other members of a family to not speak with another family member as toxic.

If it's demanded yes, but there needs to be an agreement between the parents because that cuts both way doesn't it. Demanding that the person who isn't allowed contact accepts the situation would also IMO be toxic.

An awful dilemma for any couple to have to deal with .