SOLVED. Protagonist pretending to be long-lost twin boy [s]

[Li]

Hi all,

I'm looking for a book that I have forgotten. I have read it sometime around 2000 but it was a rather old book. I can't remember the title nor the author of the book and I only have a hazy memory of the plot. The summary is as follows:

There is a family with 2 sets of twins - older set are boys and younger set are girls. One of the older twin boy is missing since long ago. The family offers(?) a reward (or inheritance?) for the return of the missing twin.

Protagonist (shortened to P for convenience) is a teen boy, could be an orphan or something. Someone (mildly related to the family, could be an uncle) approached P and wanted him to pretend to be the missing twin (for the inheritance or reward?). P was taught about the related history, habits, knowledge so that the family will accept him as the missing child.

As expected, the family really thought of him as the missing child except the twin brother. That family also happens to have an uncle who ran away from home long ago and an old, senile(?) relative commented that P resembles the runaway uncle, their stature and his love for cooking.

Fast forward through the story, for some reason, P went to somewhere remote (canyon or abandoned mine), found something which belonged to the original missing twin or a set of skeleton. Somehow realised the missing twin had been dead all the while. P confronted the twin brother and found out that he was the one who killed the missing boy. That was the reason for all the animosity brother had towards the outsider. Twin brother had wanted to kill P but was stopped (by someone or something that occurred)

Fast forward till the end of the story, turns out that P is actually the son of the runaway uncle. Scamming uncle was arrested(?) and the truth about twin brother killing the missing brother is uncovered.

[Sue]

Not all the details match, but I think this must be 'Brat Farrar' by Josephine Tey.

[Li]

Yes, that's the one. Thank you very much Sue! =)