In a focus group, how would you distinguish those that are familiar with each other from those that are not?

From what I read from the text “it is beneficial to avoid people who know each other, as peer pressure or values could influence their participation”. As a good researcher conducting a focus group for your research, what can be done to prevent familiarity of these group members, in order to get an effective result?

In the process of recording an event, either focus group or the semi-structured interview, what if the recording device could not record most of the important information given by your participants. What advice should be given to the researcher in this critical condition?

It may not necessary be the fault of the device, it may be the location or position where the device was placed which resulted in not getting all the events that occurred