The short answer is, yes.

Consider the AAR Article below:

FACTS:
The Seller of a residential property received two offers on her property. The Seller sent out the AAR Multiple Counter Offer form to both Buyer 1 and Buyer 2.

Buyer 2 sent “counteroffer #2” to the Seller.

Buyer 1 did not accept the Seller’s Multiple Counter Offer terms.

The Seller wants to proceed with the terms of counteroffer #2 submitted by Buyer 2, but refuses to sign the original Multiple Counter Offer form stating a signature on the Multiple Counter Offer form would negate counter offer #2.

ISSUE:
Should the Seller sign the Multiple Counter Offer form?

ANSWER:
Yes.

DISCUSSION:
Lines 8 – 11 of the Multiple Counter Offer states: Acceptance of this Multiple Counter Offer by Buyer shall not be binding unless and until it is subsequently finally accepted by Seller and the final acceptance is delivered per Section 8m of the Contract to the Buyer’s Broker within the time specified (“Final Acceptance”). Until Final Acceptance, the parties understand that the Premises can be sold to someone else and/or either party may withdraw any offer/counter offer to buy or sell the Premises.

Lines 40 – 42 states: SELLER FINAL ACCEPTANCE Signature by Seller below and delivery to Buyer or Buyer’s Broker as indicated above creates a binding agreement.

Therefore, the Seller would be required to sign the Seller Final Acceptance portion of the Multiple Counter Offer to be bound to the contract and proceed with Buyer #2.

Original Article from AAR Online:
https://www.aaronline.com/2016/03/10/seller-must-sign-and-deliver-final-acceptance-section-of-multiple-counter-offer-form-to-create-a-valid-contract/