What I tried to say to you in the beginning and others are leading to in their responses.

Buying and Selling Businesses is not something you should get involved with once.

You don't state why this is only time you will do this, but my suggestion might be not to do in once.  Then you don't have to learn.

This is a coaching moment for a professional (teaching client) and you as a professional can be held responsible for what is put on the returns.  You have basis determination for Dad.  Basis determinationf or Son.  Interest Income and Interest Expense in each year.  And, you have a related party transaction.

Potentially a rental agreement in the future.

Lots of things for which you can be lead astray.  

Get advice and advising your client appropriately should be top priority.  Not figuring out what line on the tax return it goes on.

We all face these things in our daily business.  I am not willing to provide that advice and the pitfalls in this forum.