Hi and welcome to Just Answer!There is no way we may skip instructions... - http://www.irs.gov/pub/irs-pdf/i1120so.pdf
A corporation must file Schedule O... for each tax year that the corporation is a component member of a controlled group.Thus - as that is related to your situation - the parent corporation files this schedule.
In your situation - because the LLC is disregarded - we have a parent-subsidiary group - as the corporation via the LLC - constructively owns more than 80% of the total stock of the Delaware C- Corporation.
Thanks. I guess there is no shortcut to understanding Sch O other than reading the instruction. :(