I think if it is with the HR team, there isn't really any need to know who your interviewer is.
"Structured" unfortunately doesn't really define the interview as such. It could be a mixture of any of the types of questions you have mentioned (competency/motivation/strengths/commercial awareness and other things like scenario-based questions too). It just sounds like its probably quite a defined interview and that candidates are assessed quite consistently through. From what I can see online, I think it sounds like it will be a bit about describing your journey (why you have made the choices you have), why law/why the firm, and then some competency questions. It might be worthwhile preparing competency answer that would cover the following qualities/competencies given they are mentioned on their website:
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