Can you DEDUCT Payments being paid on a PRINCIPAL ONLY Note ?

[Michael Morrongiello]

Situation;  Elderly Seller bought their Triplex home for around $350K Many Many Years ago. She lives in One unit and rents out the other TWO Units. Today its value is around $1.4M +/- 
She has discovered that IF she sells for Cash she will have a significant Tax Bite on the Capital Gain at BOTH the Federal and State Levels.
She is open to doing a Seller Financed Installment sale;

EG. $1.4M Purchase Price, $200K Cash Down, Balance of $1.2M financed at $4K per month for 300 Months (25 Years) - ALL Principal payments - NO INTEREST

NOTE: if the buyer was buying for cash or obtaining Bank Financing - they would NOT agree to pay $1.4M but likely a lower price closer to $1.1M or < LESS as a purchase price.

Q- The Buyer intends to OCCUPY the same unit that the seller was occupying and then continue to rent out the other (2) TWO Units.
However IF the seller is financing $1.2M @ $4K per month - ALL PRINCIPAL - Can the BUYER Deduct any of those PRINCIPAL ONLY Installment payments of $4K per month as if they were paying on a more normal Bank Financed Loan which would carry interest ?

Reason is the buyer makes good income and would be benefit from the INTEREST DEDUCTION Write Off against their Income.
Thus is weighing whether it might be better to INCLUDE INTEREST in the seller financing or simply pursue getting Bank financing so that they can DEDUCT the interest on that Bank loan (likely with a Lower Purchase price of the property also involved)

Not sure of the Tax Implications on this QUESTION ???