I do “favors” all the time for my spouse. But your long winded answer makes no sense either. “Brother, why don’t we go in the kitchen, you can tell me about a happy memory and I’ll make you some tea,” is better than leaving his brother alone to go disrupt what someone else is doing to make something soothing for Her bil who isn’t a guest, he lives there.

However; Since I posted this, she commented that her husband was working and came out to ask her to make a soothing drinking when he heard his brother sobbing. If her husband was working from home, I do understand him suggesting her to make something and spend time with his brother.