Is it obligatory to make up prayers for the deceased who was unable to perform them before death, and what is the ruling on children's negligence in that regard?

May Allah have mercy on your father. It was obligatory for him to pray according to his ability as long as his mind was sound, and you erred by not asking the people of knowledge. We hope that Allah will forgive him due to his ignorance.

Increase your prayers for his forgiveness, supplications for him, and charity on his behalf. No expiation is required for him for abandoning prayer, and it is not prescribed to make up the prayers he missed. Do not give out expiation for fasting from his estate if he was excused due to his illness, and ensure the share of those who have not reached maturity and those who do not agree.