There is a Recognizer tab in the tab pane at the right-top. The list of recognizers (extensions that perform some automatic recognition task) in that panel, contains a few recognizers you could try.
For the recording of the group conversation you could try the recognizer labeled “Speaker analysis component to diarize etc…”. This is an online recognizer, your file will be uploaded to a server and processed there. There is one recognizer which runs in ELAN, on your own computer and it is named “Silence recognizer MPI-PL” and you could try this one (or one of the other, online speech/non-speech recognizers) on the individual recordings.
In both cases it is best to start with a small, short file to find the best settings.
Also, these recognizers only produce segmentations, not a transcript of the speech (these are not ASR extensions).