Is it permissible for her husband to perform Hajj first or to pay off his debt, and what is the ruling concerning her debt for her Hajj, knowing that she has three daughters, does not possess money to cover the costs of Hajj, and cannot sell her apartment at the present time?

Hajj is only obligatory for the one who is able. So, whoever is in debt and has not yet paid it off, and does not have enough for the expenses of Hajj after paying off the debt, is not considered able, and it is not obligatory for him to borrow money for Hajj. Paying off debt takes precedence over performing Hajj.

The expenses of Hajj are not among the religiously obligatory duties of a husband towards his wife.

If the wife does not possess the expenses for Hajj, it is not obligatory for her. However, if she owns a dwelling that is surplus to her basic needs and her husband provides for her, then she must sell this dwelling to perform Hajj with its proceeds.