Well, I have presented this brick wall here before, but (at the risk of boring anyone), I'm more than happy to give the details again

My g.g. grandfather was
William MARTIN. He first appears on any record that I have found marrying Mary WOOD on 10 Feb 1833 at St. Nicholas Church, Plumstead, Kent, and I have a copy of the parish records, and the witnesses to the marriage were Thomas MARTIN and his wife Amy MARTIN (nee WOOD) (Amy was Mary's sister, and both came from Chipping in Hertfordshire). Both were shown "of this parish" and were married by banns.
On the 1841 census (Eltham HO107/482, Folio: 8, Page: 10) he is listed aged 30 and is shown as being born in the county. They are living in "Friths Buildings" in Eltham, which was a small cul-de-sac off Eltham Hill, where Eltham swimming baths now stand. There are a few other MARTIN families close by, but I've never established a relationship. There is a Sarah Martin (b. 1832) living with them, who isn't shown on the parish register, and who never appears again, so I'm wondering if she was a niece, or maybe she was an illegitimate child ?
On the 1851 census (Eltham HO107/1590, Folio: 461, Page: 4) William is shown as being 46 years old, and Mary 43. His place of birth is recorded as "London". They are still living in Friths buildings.
On the 1861 census (Eltham RG9/412, Folio: 44, Page: 3) they are both living in Eltham High Street with Mary's widowed sister Amy, who is running a grocer's shop. William gives his place of birth as "London, Middlesex, England".
William MARTIN died of Phthisis (TB) in the Greenwich workhouse on 15 March 1866, in the presence of his son. Mary had already died on 30 January 1864.
Thomas MARTIN (William's brother) first appears with his marriage to Amy WOOD on 24 January 1830 at St. Mary's church in Lee, Kent. I have a copy of the parish records, and the witnesses were a Louisa Strachan and a John Hearndon. I haven't been able to trace Louisa, but John Hearndon was the church sexton, so Louisa may also have been a casual witness. Both were shown "of this parish" and were married by banns. The IGI shows several other MARTIN families using St. Mary's church, but I doubt if they were relations if Thomas & Amy had to resort to casual witnesses.
On the 1841 census (Eltham HO107/482, Folio 10, Page: 4) Thomas is living with Amy in Eltham High Street, apparently sharing a house with Roderick COSLETT, who was a fairly accomplished artist of his day. Thomas says that he was born in the county.
On the 1851 census (Eltham HO107/1590, Folio 483, Page: 4) Thomas is still in Eltham High Street running a grocer's shop, and he gives his place of birth as Plaistow, Kent. Amy is incorrectly transcribed by Ancestry as Mary. They have the GOSLING family living with them, but I can't find any family connection.
Thomas MARTIN died sometime around 1856, but I can't find a death record for him (it was definitely before the 1861 census) - I've tried twice, and twice got the wrong man. His wife AMY died in Maidstone lunatic asylum in 1864.
There are quite a few MARTINs listed in the St. Johns Eltham parish records, including the children of William MARTIN and Thomas MARTIN (Thomas & Amy only had one child, who lived 1 day). However, before about 1820 there don't appear to be any MARTINs at all, so they must have migrated into the area (well, all except John Martin, b.1808, who was born in Eltham).
I know so much about these people, but I can't trace where the male side came from ! Any help gratefully received

P.S. I can't even say for sure that Thomas and William were brothers, but I do know that Mary and Amy were definitely sisters.