All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The debtor whose loan is due or will become due before he returns from Hajj cannot perform Hajj without the consent of his creditor.
Ibn Qudaamah said in Al-Mughni: “Whoever intends to perform a trip or journey and is indebted by a loan which will become due before he returns can be prevented by his creditor.” If the creditor wants to prevent his debtor, the due date of the loan can be considered. If it will become due before his return, such as the person who travels to Hajj will come back a month later and his loan will be due during Hajj months, then his creditor can object to his traveling because he can incur some losses due to this delay. In this case, the debtor can either ask somebody to guarantee his loan - provided this person is materially and physically able to do so - or give something of value equal to or exceeding the debt as mortgage. Having secured his debts he can go, otherwise he should not unless his creditor allows him. But if he intends to return before the loan becomes due, then he can go and his creditor does not have the right to prevent him.
Nevertheless, he can prevent him if the trip is for Jihaad, as there is fear of losing one's right due to the death of the debtor.
Ash-Shaafi’i is of the view that the creditor has no right to prevent the debtor from traveling or to ask him to provide any warrantor as long as the loan is not yet due.
Al-Hattaab said that “the creditor can object to the Hajj travel of his debtor if the latter cannot pay his debt otherwise he does not prevent him.”
Now if the debtor dies leaving some property, then the first thing to be done is to pay his debts. After the payment of the debt, his will is fulfilled. Only then could his inheritance be divided among the heirs. Allah Says (what means): {…after any bequest he [may have] made or debt.} [Quran 4: 11]
But if he does not leave anything, then his relatives do not have to pay his debts. But if they do so, it is highly recommendable and highly rewarded as paying the debts of the deceased makes things - after death - easier for him and the opposite is true.
Imam Ahmad reported from Sa’d Al-Atwal that he said: “My brother died and left 300 Dinars and he left small children, so I wanted to spend on them. But the Prophet told me “Your brother is confined because of his debts. So, go and pay on behalf of him.” So, I went and paid his debt then I came to the Prophet and said: “O Prophet of Allah, I paid everything except two Dinars that a woman claims and has no proof. The Prophet said: "Give her as this is an alm.”
On the other hand, it is not obligatory on you to forgive him but if you do it would be good as it will dispel your brother's grief by canceling his debt. Imam Ahmad reported that the Prophet said: “Whoever grants an insolvent person a respite or cancels his debt, Allah Will Cast His shade on him (on the Day of Judgement).” Mu’aawiyah said: “On the Day where there is no shade but His.” It is also reported in a sound Hadeeth that the Prophet said: “…And whoever dispels the worry of a person in this life Allah dispels one of his worries on the Day of Judgement.”
Allah knows best.