Is repentance sufficient for settling a financial amount taken from two banks, given the inability to return it, and will the person be held accountable before the owners of usurious institutions?

What you did by taking money from the two banks is forbidden, because it is consuming people's wealth by false means, even if they are disbelievers. If a Muslim enters the lands of disbelievers with a covenant and trust, it is not permissible for him to betray them or take their wealth. You are obligated to return the money to its owners, because one of the conditions of repentance is to restore injustices and rights.