The ruling on one who stoned the pillars on his own behalf and on behalf of his father, and then left off the stoning

Question:
A man says: He and his father performed Hajj last year, and they stoned the pillars on the Day of Sacrifice, both of them. Then, on the eleventh and twelfth days, he stoned on behalf of his father and for himself. However, the problem is that on the eleventh day, he only stoned the middle pillar on behalf of himself and his father, and likewise on the twelfth day, he only stoned the small pillar on behalf of himself and his father. This was due to his ignorance and following the ignorant among people. What is required of him, knowing that he did not perform Hajj this year?

Answer:
He owes a sacrificial animal, and his father owes a sacrificial animal, each of them for leaving off the stoning. He slaughters for the omission of combining [the stoning]; he slaughters in Makkah. He should think of a trustworthy person to slaughter on his behalf. As long as he offers a sacrifice out of fear, whether two, or a group, or a number, for his omission of the lawful stoning. May Allah help us; there is no power or strength except with Allah.