What are the limits of interaction between a husband's father and his son's wife, especially regarding his request for her to massage him?

The husband's father is a mahram to his son's wife, based on the Almighty's saying: "And let them not expose their adornment except to their husbands or their fathers or their husbands' fathers," and His saying: "and the wives of your sons who are from your own loins." Therefore, it is permissible for her to massage some parts of his body if he needs it, as long as the touch is without lust and there is no fear of temptation.