Do I have marketing people in-house to handle digital marketing activities effectively? Or should I hire an agency and/or freelancers?

It depends on how big your budget for online marketing is and how frequently will you push campaigns online. Assuming you have a reasonable budget for online I would recommend having it done in-house for a number of reasons

1. Campaigns launch much faster when it's in-house since you don't need to depend on an agency with their own timing and schedule to launch your companies campaigns. 

2. Adjusting or stopping campaigns is done frequently and for a number of reasons. You save time and money when it's done inhouse since it would take an hour or two rather then emails back and forth causing a delay of few days sometimes which means wasted money

3. When it's done in-house your staff understand the company and have a stronger experience inside the company than the agency does, this helps configuring campaigns to reach the audience you're looking for and avoids a lot of agency/company misunderstandings