I suppose I might also have been thinking of The Unknown Ajax when thinking about Heyer’s tendency to focus on family dynamics [with regard to Venetia]. It’s one of my favorite Heyers and has been reprinted (along with A Civil Contract, currently awaiting a re-read). The Unknown Ajax is definitely a family story rather than a romance, though it does contain a romance. The family in question is turned upside-down when the aging patriarch summons the new heir, previously unacknowledged because his father had the gall to marry a weaver’s daughter. A former Army officer, Hugo amuses himself by playing dumb (and hamming up a thick dialect, which is unfortunate) while learning the many ways in which the Darracotts of Darracott Place are dysfunctional. This leads to possibly the best, or at least most gripping, of Heyer’s plots; the last few chapters are excitingly tense in a way that few of her other endings are. Hugo is probably too perfect, but I just don’t care; The Unknown Ajax is great fun and wonderful comfort reading.
(Oh, and Lady Aurelia has to be one of the models for Alys Vorpatril.)