Which attack occurs first: nucleophilic acyl substitution or nucleophilic substitution?
The answer is - it depends. On the conditions, on the solvent, on the nucleophile being used, on which ester is being used. You may get selectivity, you may get attack at both sites which generates a mixture.

In the real world of chemistry you often don't know for certain until you run the experiment unless someone has published an exact procedure for the transormation which you follow.