Please indicate if I am interpreting FAR 28.101-1 correctly.
This response is based on the information provided. We suggest you discuss with your contracting team, program manager and/or legal department as appropriate.
We believe you should notify all offerors of the apparently successful small business offeror(s). The point is to get a protest and resolve it before award. If we do not tell offerors, they will still be able to protest this point after award. We think the applicable language is in FAR subpart 19.3, particularly "FAR 19.301-1(f) The contracting officer shall accept an offeror’s representation in a specific bid or proposal that it is a small business unless (1) another offeror or interested party challenges the concern’s small business representation or (2) the contracting officer has a reason to question the representation. Challenges of and questions concerning a specific representation shall be referred to the SBA in accordance with 19.302."