Is it permissible to take something without charge in lieu of a debt not acknowledged by the debtor, and is it obligatory to inform one's father about what happened to the money that was entrusted to him, knowing that it was spent on the mother and siblings?

Your handling of the trust is a betrayal of it. You must repent to Allah and return the money to your father, bearing responsibility for its loss. If you cannot recover the money except through a stratagem, there is no objection, and this is a matter of al-Zafar (gaining what is rightfully yours by force or trickery if the other party refuses to give it). The entrusted amount must be returned in full to your father if he is alive, or to his heirs if he is deceased. Whatever was spent from it on your siblings and mother will be deducted from the amount if your father permitted it; otherwise, it will not. You must immediately abandon the idea of suicide, for it is a grave crime.