let me knock off the first two questions since they are easier
Q: Would he file taxes separately even though he is a dependent and a college student? YES
Q: If he does need to file separately does the $12,400 standard single exemption apply?
For 2019, the standard deduction amount for an individual who may be claimed as a dependent by another taxpayer cannot exceed the greater of $1,100 or the sum of $350 and the individual's earned income (not to exceed the regular standard deduction amount).
so it would be dependent on whether he has a job or not.
