There are no Partners. This sale is between the two People; it does not affect the Corporation.
If I sell you my shares of Ford Stock, that doesn't impact Ford.
You don't Write a check as business. The Buyer pays the Seller. There needs to be an Evaluation, since this stock is not publicly traded. That way, the Seller has a reportable gain or loss.
You and I own 50/50. The valuation is pegged as $100,000. So, I want to buy out your share. Well, you already Own 50%. Giving you 50% from the business is giving you your share, not buying you out. Buying you out is my Paying You Personally for the value we determine you own, because the corporation is not part of this purchase/sale.
You all need to work with your own CPA for this. It seems you are heading down the wrong path for handling it.