When it comes to a person's marriage. You have to be cautious crossing into that territory. If you approach your sister-in-law, you could cause great damage to her home. What happens if your brother comes home and your sister-in-law physically harms him? Because she's tired and hurt already. It's better to speak to your brother and pray for him to come out of the darkness. Since your sister-in-law has dealt with your brother cheating and chose to stay. Then just as she found out before. She will figure it out again. You must pray even before you talk to your brother. It's a toxic relationship but it's their toxic relationship, not yours.
When it comes to a person's marriage. You have to be cautious crossing into that territory. If you approach your sister-in-law, you could cause great damage to her home. What happens if your brother comes home and your sister-in-law physically harms him? Because she's tired and hurt already. It's better to speak to your brother and pray for him to come out of the darkness. Since your sister-in-law has dealt with your brother cheating and chose to stay. Then just as she found out before. She will figure it out again. You must pray even before you talk to your brother. It's a toxic relationship but it's their toxic relationship, not yours.