That's one of my favorite quotes. Forgiveness is such a complex, intimate subject -- especially when the situation is extreme (either in incidence or intensity) and/or involves someone lacking the repentance, restitution, or responsibility that go into personal accountability.
Personally, it took me a long time to realize I could forgive a person his/her toxicity privately and separate from condoning the crime(s) or seeking reconciliation (and therefore not subject myself to further harm). I think forgiveness is a privilege, not a right -- and there are times it's healthier for a person not to forgive, at least for a period of time so they can process and heal. It's a person's private heart matter -- one of many steps on his or her unique life path to walk.
On that note... I think one of the most harmful things you can do to someone is try to pressure or guilt him/her into forgiveness, reconciliation, etc. While doing this, people typically mention "family blood" or quote religious references, which naturally insinuates they consider you deficient in warmth, heart, morality, or some "special" insight (even if that's not their intent). Just horrid (double whammy on top of the pain you already feel). And when you are a third party, in your ignorance, you may be causing harm or perpetuating evil when you intend the opposite. Even in "families," you could have no idea what goes on behind closed doors (even siblings' experiences can differ). Blessings and healing to all who have endured these earthly hells.
"Your children are not your children.
They are the sons and daughters of Life's longing for itself.
They come through you but not from you,
And though they are with you yet they belong not to you." ~Kahlil Gibran
Again, complex and intimate subject; respect from one being to another goes a long way.