How does a person afflicted with urinary incontinence ( سلس البول) make up for prayers missed over one or two days, and is he required to perform Istinja' (purification after urinating) and Wudu' (ablution) for every prayer despite the hardship, and is he excused in this regard?

The person afflicted with سلس (urinary incontinence or chronic discharge) is like others in how they make up missed prayers (fawāʾit). They should make up as many missed prayers as they can each day, while observing the proper order. Some jurists are of the opinion that it is obligatory to make up at least two days' worth of prayers per day if there are many missed prayers.

As for the ruling on whether a person with سلس can pray more than one prayer with a single ablution (wudūʾ): The majority of jurists from the four schools of thought hold that a person with سلس may pray as many obligatory (fard) or supererogatory (nafl) prayers as they wish, whether performed on time (muʾaddāh) or made up (maqḍīyah), with a single ablution, as long as it is within the time frame of that ablution and they have not incurred any impurity other than the سلس. However, according to the Shāfiʿī school, a person with an excuse (like سلس) may not pray more than one obligatory prayer with a single ablution.