Breastfeeding baby, behind mom's back!

I was watching a video on snapchat about a man who found out his wife was secretly breastfeeding her SIL's baby (nephew). The mother of the child had to switch to formula due to health reasons. The wife and her mother didn't like the decision and argued with the child's mother (brothers/sons wife) about her decision. The husband said when he confronted his wife and she felt that breast was best and that she was only giving back to the baby what his mother was depriving him of. The man was conflicted about whether or not to say anything because his wife didn't want to be cut out of the babies life.

1. As a man would you let the mother know what had been happening?

2. As a mother how would you react/ respond upon hearing the news? How would you feel?