turkey poult sneezing

If it is just the odd sneeze then he/she could have dust in her nostrils but any more than the odd one I would seek antibiotics.
Ideally he/she should be seperated from the others and perhaps a course of something like baytril should be started. It could have the start of a respiritory infection and it isn't worth taking the risk of passing this onto the other two.

yes it sounds like it could be the start of mycoplasma or similar. Get an anti biotic as soon as possible and treat all three, as they have all come down with it then you can keep them all together. Fingers crossed that in a week to ten days they should be OK. However if it is myco they will never be cured so any stressful time can make it re-emerge.