Having taken a quick look across Hill Dickinson's website, I think it's clear you have to choose only one of the three broad groups for your TC. However, then you get to choose between a number of different seats offered by each group. The way I see it, the question can be interpreted in two ways depending on what is meant by the term 'teams':
- Which practice area in which group are you most attracted to?
- Which of our groups are you most attracted to?
Your approach seems to track the first formulation. Intuitively, I think this first interpretation is likely the right one, since if the second interpretation was right using the word 'seat' would be completely superfluous.
However, I would also look at this from a upside/downside risk perspective. If all the firm wants you to do is explain your motivation for one of the groups, and you also explain your motivations for a practice area within a group, it should not hurt your chances too much. If anything, the more specific interest in a practice area can support a point about your more general interest in the group. If however the firm does want you to discuss a practice area interest as well and you only discuss your interest in one of the groups, you will have missed out on one of the key points of the question.