Hah...I'm lost.
How about if that same couple had $24Kish of that $100K income put in a 401K and another $6800 or so put into an HSA? Would they then be in a 0% capitals gains bracket?
As you can see, trying to figure out how this basically works.
1) Are you familiar with how your W-2 works, in terms of your gross income and the various pre-tax and post-tax deductions that you may have?
2) And then how Form 1040 works?
Start with #1, and once you understand what goes on Form 1040 Line 7, go through the rest of Form 1040.
Opening up the tax black box and looking inside is probably the best way to become unlost.