It is obvious to you that taking riba based loans is haraam, and that it is a major sin which incurs the wrath and punishment of Allaah, and the one who does that is given a threat of war from Allaah. Hence the one who resorts to that rarely succeeds.
Based on this, your father has to repent to Allaah and regret what he has done, and resolve not to do it again in the future.
Your father should look for means of getting the money he needs, such as tawarruq, which means buying something to be paid for in instalments, then selling it to someone else for a lower price to be paid in cash. Thus he will be able to get money with which to pay off what he owes. Or he may deal in salam, and sell a known amount of produce on the basis that he will hand it over after one or two years, and take the money for it now.
The Prophet (peace and blessings of Allaah be upon him) said: “Whoever pays for something in advance, let him pay in advance for a specified measure and a specified weight, for a specified amount of time.” Narrated by al-Bukhaari (2241) and Muslim (1604).
If he cannot find any permissible means of getting the money to pay off the debt, and that will result in him going to prison and losing the land that is mortgaged to the bank, then this is a case of necessity which makes it permissible to engage in riba.
See question no. 94823 for the guidelines on what constitutes a necessity that makes it permissible to engage in riba.
If your father can take the loan himself, then it is not permissible for you to engage in riba under any circumstances; if he cannot take a loan, we put your question to Shaykh Dr. Khaalid al-Mushayqih (may Allaah preserve him) and he replied that it is permissible for you to take a loan in that case. He said: Undoubtedly riba is haraam and a major sin, and the one who does that is cursed and in a state of war with Allaah. Because that is the case, one should try to avoid it. But the principle is that cases of necessity make forbidden things permissible. If that will lead to harmful consequences for the father, whether it is prison or a penalty and so on, then it seems that there is nothing wrong with it, but if they can find a better way such as a loan and salam and so on, then that is preferable.
O Shaykh: the necessity in this case applies to the father and not to the son; is the ruling the same?
He said: Yes, the ruling is the same. End quote.
We also asked Shaykh Dr. ‘Abd al-‘Azeez al-Fawzaan (may Allaah preserve him) the following: There is a man whose father will be imprisoned because of debt; can he take a riba based loan to save his father?
He replied: If he cannot find any other way, then I hope that there will be no sin on him because of necessity but he should hate riba in his heart. End quote.
And Allaah knows best.