It's not clear why the S Corp would attach F.8858 to the K-1.  In general, there is no requirement to attach F.8858 to K-1, K-2, or K-3 to be provided to shareholders.

Direct and indirect ownership for purposes of F.8858 reporting is determined based on attribution rules from §958(a).  Indirect ownership attribution, however, generally stops with the first US person in the ownership chain, S Corp in this case, pursuant to §1.958-1(b).

If you refer to item 6 under "Who must file", you will see that the following [emphasis added]:

A U.S. corporation (other than a RIC, a REIT, or an S corporation) that is a partner in a U.S. partnership, which is required to file a Form 8858 because the U.S. partnership is the tax owner of an FDE or an FB. Even though the U.S. corporation is not the tax owner of the FDE and/or the FB, the U.S. corporation must complete the entire Form 8858, including lines 1 and 2 of the identifying information section and report its distributive share of the items on lines 10 through 13 of Schedule G for each FDE and FB of the U.S. partnership. The U.S. partnership must furnish all information necessary to the U.S. corporate partner for the partner to complete the entire Form 8858.

If the intention is to treat USC as an indirect tax owner, there would have been no need to explicitly impose a filing requirement on USC and highlight that USC would be required to file even though it is not a tax owner of the FDE/FB.

IMHO, filing the F.8858 with all its full glory with a 1040 will just create unnecessary confusion.  This being an engagement you are personally responsible for, you would be right to raise questions and do more research before deciding how you may like to proceed.