I have noticed myself while transcribing that certain pics should be linked. In those cases in the notes section, when transcribing, I mention that a relative of this particular transcription has been transcribed prior. It may give the researcher the incentive to keep looking for more family members, thus boosting BG and the team. (Being the photographer and the transcribers).
I hope this may help solve the situation until BG comes up with a link/de-link function perhaps.