They’re both pretty. It’s just that Krystal takes more after their dad while Jessica takes more after their mom. Krystal is also taller, which makes her proportions seem more even. Regardless they’re both gorgeous

I’ve had braces and it’s physically impossible for braces alone to change your jaw permanently.
My jaw orthopedic told me about this due to my jaw related issues from rubber bands on braces. What they do is force your jaw into an unnatural position, which strains your jaw muscles and only make them bigger (similar to people with uneven jaws due to jaw clenching). Braces can’t permanently fix an over or underbite. You need to get a surgical procedure to either elongate or reduce the jaw bone, as well as wear braces for an additional time to reposition the teeth to fit the new bite.
Note that this surgery will only push the jaw further ahead or back by reducing/elongating the middle part, no reduction of the bone as performed in typical jaw shaving is done to give the result that Jessica has. It’s only noticeable from profile.