Why are you so convinced that the Wentworth brothers are younger sons as well as the Admiral? Donīt you think the eldest Wentworth son would have been mentioned if there had been any? Why did Mrs. Croft only talk of the married curate when there had been another married brother (because being the eldest one he would have been married most probably)?
And if the Admiral had an elder brother wouldnīt he have justified his search for a house in Somersetshire with the desire to live near his relatives instead of reasoning that this was his birthplace?
Perhaps I am being misinformed but I am not convinced yet...