What is the ruling on a husband's jealousy of his wife's brother through rada'a (nursing), and his telling her that she could lose him because of him, and how should this jealousy be dealt with, taking into consideration the noble Hadith: "What is forbidden by lineage is also forbidden by rada'a (nursing)"?

Suckling renders unlawful what birth renders unlawful. Thus, it permits a man to look at, touch, be alone with, and travel with his suckling sister, unless there is suspicion or fear of fitna (temptation/strife). Embracing and kissing are disliked, especially kissing on the mouth, between siblings whether by suckling or by lineage. The husband is advised to exercise wisdom and caution, and the wife to be moderate in her dealings and jealousy, while avoiding excessive jealousy.