In a non-emergency situation what would be the din of a daughter aiding her ailing father in-law and a son aiding his ailing mother in-law.
It is formally permitted for a daughter to aid her ailing father-in-law, and vice versa, even in a non-emergency situation.
Aiding an ailing person does not involve a “maga chibah” (“intimate contact”), and based on the Shach and later poskim, it will not involve a formal prohibition.
However, like most medical matters, it is certainly preferable that a man should aid a man, and a woman a woman, where this is possible and convenient. If there is a strong preference for a family member, however, this will not be an option.
The fact that the person involved is one’s father-in-law or mother-in-law does not make a difference to this ruling.