I have a c-corp that's the sole member of a subsidiary LLC. Would tax returns be consolidated under the C-Corp or would I file 2 separate returns? Can I use Turbotax?

I highly recommend you seek professional assistance to get educated in how the returns need to be filed and see what state rules also apply.   Once you know how it needs to be completed the Turbo Tax program may be an option.

TT Business will not run on a Mac.

Definitely.  You only file a single C corporation tax return.

Since the C corporation is the sole owner of the LLC, the LLC is considered a disregarded entity.  In this context, the LLC is now treated as if it were a division of the C corporation.

Treating this as a division is different than if it were a subsidiary.  If this were a subsidiary, the C corporation would be eligible to file a consolidated tax return.  A division is just included in the C corporation activity and no consolidated return is filed.

Hopefully the above is clear and you understand the difference between the division filing and a consolidated return filing.  Division filing is one single tax return.  A consolidated return filing is multiple company returns that get pulled into one single consolidated tax return.  The consolidated tax return filing is much more complicated.