How does one pray if they suffer from involuntary urination and their clothes become soiled by urine, given the difficulty of changing them for each prayer?

Your father is considered to have perpetual ritual impurity ( سلس البول) as long as he cannot control his urine and urination is continuous, or if it stops for a period insufficient for purification and prayer. He must perform ablution (Wudu') at the beginning of each prayer time, and what is discharged thereafter does not harm him. If it is difficult for him to wash or change his clothes for each prayer, he may pray in them as they are, to avoid hardship, according to the Maliki school of thought. He must maintain his prayers, for what he is experiencing is not an excuse to abandon them.