What is the ruling on making up 12 years of missed Ramadan fasts, given that the person is elderly, has repented, and is unable to make up the fasts by fasting? Can he expiate for that with his money? And how much is the expiation for one day, and to whom is it given?

There is no difference between your question and the previous one. Your father broke his fast for twelve years, and the other for four years, and the answer is the same. The expiation for delaying the make-up fast is to feed one poor person for each day that its make-up was delayed until the next Ramadan arrived. This expiation is not repeated for the same day. Since your father delayed the make-up for all those years, he is obligated to offer expiation for delaying for each day by feeding one poor person a mudd of food, and another mudd as compensation for the make-up he was unable to perform.