Retirement tax questions

The question occurs to me (though thankfully hasn't happened in my particular case with an inherited IRA) what if a taxpayer has their own IRA and an inherited IRA, and they both have a basis?  That is, the amount of tax already paid needs to be subtracted proportionally when calculating the taxes on the distributions.  Do two separate Form 8606's need to be filed?  If yes, does TT generate both forms?