I will agree with TaxGuyBill but add - if the transaction is between the two brothers then it has no effect on the company books.  Example - prior to sale 100 shares outstanding, owned 50 and 50 by each brother.  Brother A sells his 50 shares to Brother B.  On the company books there is still 100 shares outstanding.  No change in the equity section of the balance sheet.  Just owned by different parties then before.

If the above example fits then your question is does the buying brother have a different outside basis in the stock versus the inside basis?  We need more facts of this situation.