The only Nelson Bland I can see in a census that could fit was born about 1898 in Halifax, but none of his siblings have the names you mention.
The problem is that you are only going on word of mouth and that is probably second hand, as we are talking nearly 100 years ago. Memories get very muddled and as we have all found, stories tend to get twisted. I spent ages trying to find my mother's cousins who she said all went to Australia when she was about 6 in 1926. She said they were her mother's relatives. Turned out in the end they were her father's, so a completely different name and although they did go to Australia it was separately and between 1929 and 1954.
As we've said there is no Sidney Bland in Cornwall in 1911 and no one at the moment seems to be able to link the names you have mentioned to one family.
I think you need to use Freebmd
http://www.freebmd.org.uk and start with the more unusual names and see if you can find births for them, then see if you can find any of the other siblings born in the same place. It wont be easy and will probably take some time. The 1911 census will help, but we are not allowed to do look ups on here. This gives you some ideas of how you can use the free index
http://www.rootschat.com/forum/index.php/topic,492718.0.htmlJan