You have to handle this situation very carefully. You can’t just go to a conclusion as this is a very sensitive matter. I would suggest you to have a talk with your wife first. Ask her the reason for her accusation against your father. You have to be very patient with her. Sometimes, when a lady comes to a new environment and a new home, it takes time for her to adjust to the new customs. There’s a possibility that she might have misunderstood any act or behaviour of your father.
Therefore, you need to have an effective communication with her on this matter. I would suggest you, listen to her point of view first. Try to hear her point of view without being judgemental. It’s important to know both sides, so after talking to your wife, talk to your father too. It might be a little hard for you to digest these kinds of accusations against your father but it is needed to know the truth. There may be a chance for your wife to be right, so try not to think like your father’s son but like your wife’s husband also.