@sjrcpa please help me understand the basis vs equity difference. their books are kept as tax books. before the transfer, Father's basis was initial Capital Stock of $100 plus all net profits (or losses) from the date of incorporation, plus Additional Paid-In Capital, less non-deductible items (charity, section 179, life insurance premiums, 50% meals etc), less distributions. so at any given moment i could say Father's basis is equal to Total Equity on S-Corp Balance Sheet. is that correct?  

Now beginning 1-1-18 this is no longer the case, because Son's basis is now $10 + 49% of what was Father's basis as of 12-31-17 but $10 isnt on the books. so Father and Son now need to maintain a spreadsheet with their basis that will only include their own distributions and 51/49% of net profits and other non-deductible expenses.
what i see in Total Equity on the Balance Sheet is not just the sum of Father's and Son's basis anymore nor is the equity proportionally split 51/49 because they did not take same % of distributions, is that right?

and another question: if Father had Additional Paid-In Capital in S Corp before the transfer, does it mean that Son is now entitled to 49% of that? APIC was included in Basis calculation, so i am assuming the answer is yes, but want to double check. should the S-corp repay it back to Father and Son proportionally or does it not matter if its on the books? they have enough basis after 2018 profits to withdraw it (or simply reclassify it on BS??)

thank you so much. I appreciate all of the help, you have no idea...