What is the ruling of Islamic law on obligating a wife to host her sick sister-in-law in her home, and what problems result from that?

A piece of advice for the wife: do not prevent her husband from hosting his sister for her care, as this involves showing kindness to the husband, maintaining kinship ties, and honoring the father. However, she is not obligated to accept her sister-in-law sharing her living space; she should have a separate dwelling.

Regarding the responsibility for her care: If she is well-off and has money, she should hire someone to serve her from her own funds. If she is poor and her father is well-off, then the father should hire someone to serve her, and her service or maintenance is not obligatory upon her brothers. If the father is poor, the more a sound opinion is that maintenance and service become obligatory upon the well-off brothers and sisters. If service is not obligatory upon the brothers, and their father commands them to do it, then it appears obligatory to obey him unless it causes them harm.