You will not get the Full Time student question for the 24 year old. Being 23, earlier in the year, is not relevant. Age at year end is all that counts.
You will only get the student question for the 21 y.o. depending on how the other questions were answered. How did you answered them. Does TT conclude that she is your dependent?
There are two types of dependents, "Qualifying Children"(QC) and Other ("Qualifying Relative" in IRS parlance even though they don't have to actually be related). There is no income limit for a QC but there is an age limit, student status, a relationship test and residence test.
A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:
- He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled
- He did not provide more than 1/2 his own support. Scholarships are excluded from the support calculation
- He lived with the parent (including temporary absences such as away at school) for more than half the year
