Yass, queen! This entire speech is just fabulous. It highlights the handwaves that come with redemption arcs, especially when the party to be redeemed was/is a prolific murderer, AND the "Too Good For This Sinful World" MCs!
Not the party who was killed, not the party who had a loved one...
Just saying tho: Sis needs to break her mum out of that self-imposed state of disbelief. Smack her with the hard truth and irrefutable evidence that her husband is a lying dolt, the woman she invited into her house is a viper, and the viper's child is an actual Devil's Egg.
Yes, concubinage...