The following info is just for Chuck.
I have no expertise outside England, it is a case of trying to discover what records are available and where they are. Forums are a great place to get ideas from, the one I use most is
http://www.rootschat.com/forum/index.php from that site I found
https://wiki.familysearch.org/en/Portal:Brazil
Research in South America looks very challenging.
A background on the history of South America with Europe would give you an understanding of why the family was out in Brazil.
Using http://books.google.co.uk/ I did a search on "British merchants in Rio history" Some of the links take you to pages in the books. I have not read all the links.
From "A concise history of Brazil" by Boris Fausto and Arthur Brakel it would seem that by August 1808 there was a nucleus of between 150 and 200 British merchants and commercial agents in Rio. Napoleon had taken over Portugal and Price Dom Joao VI of Portugal moved his entire court to Brazil, up to 15,000 people sailed to Brazil in Portuguese ships escorted by a British fleet. Joao opened Brazils ports to friendly nations, Great Britain being the chief beneficiary.
From similar searches on the main google site, I found that an English church was built in Rio de Janeiro in 1820.
Again I have no expertise in merchant shipping. I wonder if there are any records concerning ships. That might be another area to explore. Even if you found no information on your Denby family it all gives useful background knowledge.
So as a starting point it MIGHT and is only a guess at best that a Denby male went to Brazil sometime after 1807 and had a family out there. He was probably British but not definitely. He was most likely a merchant.
Doing a general google search on "Denby Brazil"
http://genforum.genealogy.com/denby/messages/310.html
Perhaps you could contact this person. I have not used this genforum site. But he has given you a few more names to go on. Of course you do not know if and how they are related. There could have been more than one Denby family in Brazil.
Armed with the new names I then turned back to the English Census.
In 1881 living in Toxteth Park
Virginia C. Thompson 45 widow born with Caroline M. 28, Juliana 24 and Robert 18 CARLOTTA ALLEN 25 visitor all born Rio de Janerio with 2 servants.
So this gives you a connection to your Barten Fletcher Allen family.
Were Carlotta and Virginia sisters, and this Carlotta Virginia's niece?
[death Mar quater 1880 George Armitage Thompson age 66 W. Derby - Virginia's husband?]
Unfortunately I have not been able to trace Virginia and her family any further.
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In 1861 living in Leamington
Sophia Thompson 41 widow Fund holder, living with Agnes Jane 13 and James G. 11 with 3 servants.
1871 living in Leeds
Sophia A. Thompson 51 property owner born Rio, Maria A. 25 born Rio, Agnes J. 23 born Birkenhead, James G. 21 iron manufacturer born Birkenhead and 3 servants.
there is a death Sep quarter 1877 James George Thompson age 28 Birkenhead
1881 living in Birkenhead Sophia A. Thompson 61 widow Lady independant born Brazil, Agnes J. 33 and 3 servants.
1891 cannot find them.
1901 living Birkenhead Sophia A. Thompson 81 born Brazil with 3 servants.
Death Dec quarter 1903 Sophia Amelia Thompson age 83 Birkenhead.
Was this another sister to Carlotta and Virginia?
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Now looking for male Denby born in Brazil I found ;
1881 John Henry Denby 57 born Brazil a retired merchant living in Leamington Priors with wife Maria Louisa 36 born USA N.York and 2 servants.
possible death 1883, John Henry Denby age 59 Warwick.
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1891 living in Kensington
William C. Denby 62 shipowner born Brazil with wife Mary 48 born Stone and 3 servants.
perhaps of interest is a marriage in Dec quarter 1882
William Charles Denby to Mary Sharp in Kensington.
This certificate should name William's father.
1901 living in Kensington
William C. Denby 73 living on own means born Brazil with wife Mary 65 born Staffs. Stone and Mary E. Sandilands 45 born Brazil, Robert B Sandilands 7 born Scotland, Mary A. Sandilands 6 born Scotland and 3 servants.
death Jun quarter 1906 William Charles Denby age 78 Kensington.
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It could be that they are all one family brothers and sisters, if so they would be :
Sophia Amelia Denby born about 1820
John Henry Denby born about 1824
William Charles Denby born about 1829
Carlotta Maria Denby born about 1834
Virginia Caroline Denby born about 1836
but this is just speculation, you need to find some other proof.
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Also found on the IGI
batch number C006383
Grace Roscoe Allen b. 28 Jul 1854 Rio De Janeiro,
Basten Fletcher Allen + Carlota Maria Denby
and for Tijuca, Rio De Janeiro
Caroline Emilia Thompson b. 6 May 1852
Julianan Carlota Thompson b. 22 Aug 1856
Jane Amy Thompson b. 20 Mar 1858
parents George Armitage Thompson + Virginia Caroline Denby
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Good luck with your hunting.
