Completing Form 7203 for shares in an S-Corp acquired by inheritance

Both my in-laws owned shares in an S-Corp 50/50 (not jointly) and held them separately in their respective trusts.  Both have now passed, the shares have now been inherited via the trusts by their 2 daughters, also 50/50.  They are also the officers and directors and the S-Corp lives on, but has a small loss every year.

While, if I am correct,  the S-Corp continues to keep the original adjusted basis of the shares (99% of  the assets is land for development) on the S-Corp returns, isn't the basis stepped up (1/2 at one parent's date of death and 1/2 at the other's)  at the shareholder level and that new basis reported on the Turbo Tax "S-Corp Shareholder Stock & Debt Basis Limitations Worksheet"  for the heirs, which is then used to file the form 7203s?  Would that new basis for each heir be entered on Part 1, Line 2 , and if not, then where?  Similarly, for each parent's trust transferring the shares (and reducing the basis to zero, would the transferred basis be the (un-stepped-up) original adjusted basis and entered on Part 1, Line 13 on each worksheet?  (Seems to be the only line possible).  Note - there are no loans from shareholders or other liabilities.