Based on those numbers, it's real simple. Your parents enter only the first 1098-T (undergrad) on their tax return and claim a full tuition credit. There's a enough in box 1 that they can claim the maximum LLC, even if they are no longer eligible for the AOC.
You enter only the 2nd 1098-T on your return and pay tax on $30,284 (51,126-20,842) of scholarship income (unless you can reduce it by books and other course materials not already in box 1). Your parents should not (and are not allowed to) report that income on their return.
You can not use any of the box 1 amount on the undergrad 1098-T to reduce the tax on the grad scholarship.
