Is the salary of one who works in a shopping center and is forced to place boxes of alcohol on the shelves lawful (halal), and is it permissible to eat at his house?

Work that necessitates aiding in the sale of alcohol is prohibited. Your sister's husband must abandon it and seek another job. The salary he received for his prohibited work must be disposed of by spending it on public interests and charitable causes. His salary takes the ruling of mixed wealth, and dealing with its owner is permissible, though disliked, so eating from his house is not forbidden.