The answer to you question is "them", because of the semicolon.
Consider the following
Mr.Ferrara will be interviewing two candidates for the position of sales director today,
both of whom are qualified for the job.
The two clauses are interdependent.
Mr.Ferrara will be interviewing two candidates for the position of sales director today;
both of them are qualified for the job.
The two clauses are strongly related but independent.
Mr.Ferrara will be interviewing two candidates for the position of sales director today.
Both of them are qualified for the job.
The two clauses are in different related sentences.
Mr.Ferrara will be interviewing two candidates for the position of sales director today because
both of them are qualified for the job.
The two clauses are related and linked by a linking word.
To help you fill in the blank, you might wanna try changing the sentence a bit
Mr.Ferrara will be interviewing two candidates for the position of sales director today;
____ are both qualified for the job.
Then you have to try and fill the blank with either they or who, which is slightly easier. The previous rules apply to those two clauses aswell.