1) You need to file the missing Forms 8606 and file amendments to any incorrectly filed Forms 8606.
2) For the split rollover that you described, the single code-G Form 1099-R must be entered into TurboTax as two code-G Forms 1099-R, one with $8,000 in box 1, $0 in box 2a and $0 in box 5 for the portion rolled over to the traditional IRA and another with $2,000 in box 1, $0 in box 2a and $2,000 in box 5 for the portion rolled over to the Roth IRA.
