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Are these people deceased?
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FreeBMD (.org.uk) is a helpful place to start.
George's birth was registered in the 1st quarter of 1932:
March qtr 1932
Southwark district vol 1d, page 25
Bird, George A J Mother's maiden name: Bangs
Using the surname of Bird, and Mother's maiden name of Bangs, there are 2 brothers, born 1933 and 1936.
I'll leave you to find these for yourself!

Marriage of parents
December qtr 1925
St Olave district vol 1d, page 305
Bird, George J
Bangs, Alice
You can use the year, quarter, district, volume and page numbers to order certificates.
Only £9.25 direct from the GRO.