Praise be to Allah, and may peace and blessings be upon the Messenger of Allah. To proceed:
First, one should believe that everything that occurs in the universe happens by the decree, will, and wisdom of Allah تعالى, and that Allah سبحانه is All-Wise and All-Knowing. Some of the wisdom behind His decrees may be hidden from us, so it is not permissible to object to His decree or resent it.
As for suicide, it is one of the major sins, and a severe warning has been reported concerning the one who kills himself. Allah تعالى says: “And do not kill yourselves. Indeed, Allah is ever Merciful to you.” [An-Nisa: 29] However, a Muslim committing this major sin does not mean that he leaves Islam if he was a monotheist and did not consider suicide lawful. Rather, he is subject to the will of Allah: if He wills, He forgives him; and if He wills, He punishes him. Then, if he dies upon monotheism, his ultimate destination is Paradise.
In this case, if it is established that he tied a rope around his neck with the intention of killing himself, then it appears to have been suicide. However, one should not definitively judge the details of his inner state or determine his fate before Allah. He may have acted out of ignorance, psychological distress, or extreme emotional turmoil, and Allah knows best about his condition and intention.
As for his parents being righteous and upright, this does not prevent them from being tested by the loss of their son. Affliction does not indicate that a servant is insignificant or disgraced before Allah. Allah may test His servants to examine their patience, expiate some of their sins, and raise their ranks. Allah تعالى says: “And We test you with evil and with good as a trial, and to Us you will be returned.” [Al-Anbiya: 35] The Prophet ﷺ also said: “How wonderful is the affair of the believer! Indeed, all of his affair is good...” Narrated by Muslim.
As for the deceased appearing in a good condition during washing and preparation for burial, this may be taken as a hopeful sign of goodness, but it is not permissible to state with certainty that it is definitive evidence of a good ending or forgiveness. These are matters of the unseen whose reality is known only to Allah.
If the deceased was a Muslim and a monotheist, it is permissible to pray for him to receive forgiveness and mercy. His family may, for example, ask Allah to forgive his sins, shortcomings, and what he did to himself. As for definitively stating that he is in Paradise or declaring with certainty that he is being punished, this is not permissible without evidence.
As for the question: Why did Allah choose this particular way for him to die? Describing it as Allah having chosen it in a manner that implies objection is incorrect. Allah تعالى decreed death and its causes, and it is not permissible to object to His decree. As for suicide itself, it is a prohibited action for which the person bears the sin. It is not correct to say that divine decree forced him to do it. A servant is accountable for his voluntary actions, and it is not permissible to use divine decree as an excuse for sins.
Therefore, what his family must do now is be patient, think well of Allah, pray for him to receive mercy and forgiveness, and refrain from delving into matters about his fate and condition before Allah that they have no way of knowing, while submitting to the decree of Allah تعالى.
And Allah تعالى knows best.