The website you stumbled across has transcripts of all JAB's BREW charts, as well as other people's contributions like the first URL you gave from George Brew of Florida (which may or may not be correct).

See: brew.clients.ch/BrewONS.htm (if it says a page not found change the capitals in the URL to lower case).
There is also a copy at: www.mannincloud.info/Brew/brew_ons.html

Your second URL was from JAB's work. He refers to the sources from the Manx Museum where he did all his family history research from primary sources.
He wrote:
'Muldonny McVriw or McBrew flourished 1406-17, "one of the Eldest and Worthiest of all the Land of Man and the Inquest of the 24 Keys". He had two sons:
•Patrick McBrew, MHK [Member of the House of Keys] in 1505, of Ballameanagh in Slegaby, Jurby. Compounded 1515. [See also "Brew of Ballavarran"]
•John McBrew, Co-owner with his son Patrick of the Guilcaugh, Andreas. They paid a fine of 23s in 1515 for their property.'
Those references should all be able to be found in MM original records.

To link back to him in your own family tree you would need to confirm each generation back from yourself through BMDs, censuses, wills, land records, etc.

JAB's trees are a good guide but you still need to prove that each generation is correct going back one by one.

Sue