You could do either. The most common reason for following one kind of qualitative interview with another is what is known as "member checking." This involves developing a set of preliminary analyses from one set of interviews and then getting reactions to your thinking via the other form of interviews.

Another strategy would be conduct some small focus groups, and then choose particularly interesting participants for follow-up interviews.

What is the phenomenon under question?

Hi Shalendra Mohanlall ,

When researchers do review the literature and previous studies, they could find the interview questions that may modify into focus group interview questions. Otherwise, you may create new questions that be analysed and synthesised from the literature review. The consequence is to answer the research question by adopting thematic analysis or content analysis based on theoretical framework or theories or variables in particular fields.