Is a sick person who is unable to move and perform ablution in the hospital sinful if he does not pray, and must he make up the missed prayers?

As long as your father is conscious and of sound mind, prayer is not waived for him. He should pray according to his ability. If he is unable to perform ablution (wudu), he should perform tayammum (dry ablution). As for the prayers he missed, believing that prayer is waived due to illness, if that was due to ignorance, we hope he will not be sinful. But if it was done knowingly, then he must repent and make up those prayers. He must also repent to Allah for any shortcomings in the matter of prayer.