Mary, as is noted in _Potato Peel Pie_, killed her mother but the jury let her off saying "lunacy". Charles took care of her thereafter, which took a lot of his money which wasn't exactly unlimited anyway. After their father died and they were able to live together again (Mary attacked Dad, too? I'm unclear), they had a salon that was attended by a long list of familiar names (covered also in _Potato_). Charles was unluckier in love than Dawsey, perhaps because he never met a woman who proposed to him.
Juliet and Dawsey connecting over the Lambs sets the stage for the entire literary society to trust their stories -- and Elizabeth's daughter -- to Juliet. They know that a woman who knows the story of the Lambs is not going to judge them harshly. And they know that such a woman will appreciate Elizabeth for the hero she was, even if she did love an occupying German soldier.
Because the story is so anecdotal, and the cast large enough to cause the reader to struggle at the beginning, it is easy to miss the significance of the Lambs to the story as a whole. So I'm leaning towards too-clever-by-half. But I don't know.
ETA: At one point, Juliet expresses a desire to have been able to write about Anne Bronte when the neighbors were still alive so she could talk to them. I'm now wondering if this is a little Easter Egg to suggest that Juliet was in part inspired by Elizabeth Gaskell?
ETAYA: No freaking way! There's a biographer of the Brontes named _Juliet_! Last name Barker, born 1958. Still!
ETAOMT: Isaac Bickerstaff is somewhat misrepresented in the book. In fact, Bickerstaff was originally a Swiftian April Fools joke. Ha!
ETASMBICLTA: Why is no one mentioning Betty MacDonald in conjunction with this book? Especially with the afraid of chickens references by both Isola and Juliet. Maybe I should go read _The Egg and I_ next. I surely loved the Piggle-Wiggle books. _Which_ have a lot of the same themes of acceptance of the weird and different.
This explains the origin of the name Isola: Emma Isola was adopted by Charles and Mary Lamb.