According to FAR 15.505, "Offerors excluded from the competitive range or otherwise excluded from the competition before award may request a debriefing before award (10 U.S.C. 2305(b)(6)(A) and 41 U.S.C. 253b(f)-(h))." In your case, you are not making award at this point, nor are you setting a competitive range. You are simply dissolving the set-aside and, essentially, going out for another round of offers. In addition, you are not excluding the either of the offerors from the competition in the further rounds.
That said, if you are not changing the requirement, you wouldn't be providing a competitive advantage to them by explaining how their proposals submitted under the set-aside does not meet the Government's requirement as stated in the solicitation. It could be to the Government's advantage, with regard to competition, to accomplish a debriefing so that they may be able to compete in the full and open acquisition. The debriefing doesn't guarantee that they will be successful when you pursue full and open competition. They would still have to provide an acceptable proposal to remain competitive.
When you receive offers in this next round, you will set the competitive range and discuss strengths, weaknesses, deficiencies, etc. with those in the range before requiring a final proposal revision. At that point, if these small businesses make it that far, the environment has leveled. Should they still be unacceptable, then you may potentially be back to providing them another debriefing. I don't see any downside to providing a debriefing to the small businesses that are currently found unacceptable.
You should discuss the matter with your legal experts and proceed having the benefit of their counsel.