It could be anything - viral, bacterial, or even fungal if you've had rain in the heat we're having here in Texas.
First, I'd buy VetRx from your local feedstore or TSC and use that (diluted) to swab all their nostrils, the cleft opening in the roof of their beaks, and under their eyes. This can help reduce inflammation, keep them breathing, break down some mucus, etc. It will help against sneezing and irritation.
I would also give them all vitamins daily, but one specifically with a good source of vitamin A. Polyvisol baby vitamins contain a good source of A and the other oil vitamins and are easily given 3 drops in the beak daily. Vitamin A is a key vitamin for respiratory healing and health. If not polyvisol (the non-iron-fortified formula - I got mine in the vitamin section of Walmart) then try cod liver oil, 3 drops in the beak three times weekly.
Also since she's sneezing, that means her sinuses are draining into her digestive tract (through that opening in the roof of the beak). She and the others should get yogurt (and its live bacteria) daily for a week. this will help prevent a secondary diarrhea or fungal infection as the drainage contaminates the digestive tract and kills off certain numbers of the good bacteria there. The yogurt contains live bacteria of the same type that colonize our birds' guts and help prevent diarrhea. iF at any time you choose to medicate, you still must give "probiotics "(living bacteria) but you can't use a high milk product like yogurt. Then you'd use acidophilis capsules/tablets (the contents of either, one per bird daily) or Probios powder or paste daily.
You could treat with antibiotics at this point. But if you do, be sure to use the 'mycins 14 days unless otherwise noted on the package. Tylan is a great product, as is LS50 if you choose to medicate. With Tylan, you can go injectable for three days (Tylan50 - which also makes a great sinus flush if you dilute in three parts water), or in the water (can't do the flush with the soluble form) and you can still use yogurt as your probiotic.
Only because of the wheezing would I consider an antibiotic this early in the game, and that's just considering one. If it continues for more than 2 days without change, or worsens, please medicate then.