"Is the amount to be entered the total balances in the THREE IRAs or just the one with the withdrawal?"
All three. For the purpose of calculating nontaxable and taxable amounts, all of your traditional IRAs are treated as one combined traditional IRA.
With about $37,741 basis in nondeductible traditional IRA contributions and around $1.5M in traditional IRAs, about $2,500 of your Roth conversion is nontaxable, about $97,500 is taxable and about $35,200 of your basis remains in your traditional IRAs to be proportionately applied to future distributions from any of your traditional IRAs
