Complex sentence: Some offices were sold with the right of succession by the heirs of the purchaser, but this could be done only in the case of an office of minor importance, in the exercise of which no special ability was required.
Split into simpler sentences: Some offices were sold with the right of succession by the heirs of the purchaser. This, however, could be done only in the case of an office of minor importance, in the exercise of which no special ability was required.