Do "research team" and "research group" mean the same thing? I see some papers use "research team" while others use "research group". Do they mean the same thing, a few of researchers that form a team dedicated to a research?
I would use “research group” to describe the set of people that is the students that I advise and any researchers I employ (plus myself). 

“Research team” to me would be primarily the set of PIs with who I am collaborating on a given grant or other project, and may also encompass the students and researchers who are directly involved in that project.

“PI” here would be anyone in a principle investigator role for the project. This would certainly include professors and researchers at government labs/museums/zoos with whom I set up the project and secured funding, and could also include people who joined the project later under their own resources at our invitation, rather than being hired by one of the existing PIs out of the original funds. A postdoc coming in with their own funding, but with the funding contingent on their having a supervisor, would be in a grey area between the “PI-level” sense of “research team” and the broader sense of “PIs plus their students and staff”.