NIIT Taxes For Spouses

I am modeling the tax impacts for the seller of a potential deal. Spouse A founded the business decades ago as an S-Corp and is still actively involved with it. At some point they transferred the shares in the S Corp from Spouse A to Spouse B. Spouse B has never been active in the business.


Because Spouse B is not active in the business will they be subject to NIIT taxes on the sale? Or are the spouses treated a single entity and therefore not subject to the NIIT tax?