Is a sister obligated to contribute equally to household expenses with her brothers in the family home, given that her salary is insufficient to meet her own needs, while her brothers are in a better financial situation and she often borrows from them?

It is permissible for a sister to be financially independent and support only herself, or to share with her brothers in the family's expenses by mutual agreement, whether the amounts are equal or different, depending on each individual's situation. If the sister's money is not enough to meet her needs, then her well-off brothers are obligated to complete her maintenance in a reasonable manner.