Is it permissible to perform Hajj on behalf of my deceased father who did not pray, and will it expiate his shortcoming in prayer?

The questioner performed Hajj three times, while the correct understanding is that the obligatory Hajj is once, and anything beyond that is voluntary. Disbelievers do not benefit from righteous deeds, and it is not permissible to seek forgiveness for them. However, if the questioner's father used to pray sometimes or if there is doubt about his disbelief, there is no harm in performing Hajj on his behalf, provided that it is conditioned on his faith. For example, one could say: "O Allah, make the reward of this for my father if he was a believer." Conditioning a matter is permissible in acts of worship and supplication.