Para 34(2) doesn’t help much and simply refers to the partner’s share of the income profits “at that time” but this will not normally be capable of an accurate calculation until after the end of the accounting period. In practice a reasoned estimate can be used but I would try and incorporate the fixed share although given that the parties are connected and associates it may not affect the SLP calculation.
Unfortunately in this case, the father isnt acquiring any shares on incorporation. As such, I cant see that the company is connected to him after the incorporfation. I think the position would be different if he acquired a single share as the father, together with the son, would togeher control the company.
A further complication is that the partnership has made a loss for the last 2 years. Therefore looking at it in actual mony terms, he has a 100% income share – although t