Younger sons of estate owners chose occupations like the church or the navy (or the law or the army) but it doesn't mean that these jobs where restricted to them. JA's father was a clergyman without an estate; two of her brothers became clergymen, too, and other two went into the navy. One of her brothers did inherit an estate, but it was the second son and it was a cousin's estate (like Frank Churchill).

He was not Mr. Wentworth, the former curate of Monkford, however suspicious appearances may be, but a Captain Frederick Wentworth, his brother, who being made commander in consequence of the action off St. Domingo, and not immediately employed, had come into Somersetshire in the summer of 1806; and having no parent living, found a home for half a year, at Monkford.(Ch. 4)

Mr. Wentwoth Sr. was dead at that time. If there was an estate, and an elder son, he would have been already the owner. Why would CW not stay with him? (note that contrary to what MarianneR writes it doesn't have to be probable that he was married, but neither is Edward yet). Why doesn't Mr. Shepard mention Mrs. Croft connection to Mr. Wentworth of ----- instead of Mr. Wenthworth the clergyman? (And, in this case, he would be Mr. Edward W, unless the eldest brother were a Sir --- W., or a Lord ----...more reason for Mr. S. to mention him)

About Adm. Croft, we only have this:

"And who is Admiral Croft?" was Sir Walter's cold suspicious inquiry.

Mr. Shepherd answered for his being of a gentleman's family, and mentioned a place; and Anne, after the little pause which followed, added --

"He is rear admiral of the white. He was in the Trafalgar action, and has been in the East Indies since; he has been stationed there, I believe, several years."(Ch. 3)

We don't know if the place mentioned was an estate (and the gentleman his owner), or if it was only the town where Adm. Croft was born.