If you know your sister slept with your husband why bother to push to try to force a confession. The whole point of a confession is that someone decides to come clean about something, so you need to leave it to your sister to decide to confess on her own terms. Since you already know the truth, if you feel certain you’re not mistaken, just go with what you know and deal with the situation accordingly. You can’t hold a gun to her head and force her to admit what she did.
How to get sister to confess she slept with my husband