]but Lydia boasts about being the tallest of the girls even though she is the youngest.

I can't see Lydia (Julia Sawalha) the tallest of the girls,I see her ,kind of, short , but she is the good humoured among them.

For the sister's relationship ,I think JA portrayed that very well. the relationship between them is very strong,no jealousy, no hatred especially that each parent has his own favorite. The two elders are very close and the two yougest as well, the only one who is lost is Mary b/c she wants to be unique and I think she is happy or convinced herself to be happy .Lizzy is full of love for her sweet Jane, I don't think she minds to see her more admired, and she is delighted to talk about her with an esteem to her friends and describe her sweet nature to them, as when she talk to Charlotte about her new relationship with Bingley :

"she is not acting by design. As yet, she cannot even be certain of the degree of her own regard, nor of its reasonableness. She has known him only a fortnight."