Can a Z-Test of Two Sample means in Excel be used to answer two separate hypotheses.

Can a Z-Test of Two Sample means in Excel be used to answer two separate hypotheses.
1) Hypothesized Mean Difference=0 (Two-Tailed) (NULL vs Alternate, ho = ha)
2) Treatment > Control (One-Tailed)
I am currently doing a Z-Test of Two Sample Means (Control vs Treatment) with Null and Alternate Hypotheses. This is used to determine if there is statistical evidence to indicate a difference between the two means using the Two Tail approach.
Question 1
Can I use the same Z-Test of Two Sample Means output from Excel to Answer Hypothesis 2 above ie Treatment > Control OR is a t-Test: Two-Sample Assuming Equal Variances the more valid approach.
Question 2
Does it matter if the sample populations vary e.g. n=100 (Treatment) vs n=50 (Control) with either tested hypothesis