I think I finally found the answer within TurboTax. It seems the way I have been calculating it is correct. Since we share the office space 50/50, I divide the total square footage in half on each of our deduction calculations.

Shared this office with someone else who also used it as a home office?

So you have a home office that you share with someone else, who also uses it as a home office.

First of all, on the "Enter the Square Footage of Your Home and Home Office" screen you saw earlier, make sure you divided up the square footage correctly so that each of you takes the correct amount of square footage for the year.