Help!

I'm completely confused about my gtgtgrandfather William BOWLER c1808, living in Denton, Lancs on the 1841 with his wife Hannah BROWN c1811 (HO107/581/4 32 20). His occupation is given as 'hatter', and I believe they and their son Edwin moved to Southwark shortly after.
I have a death cert for Hannah dated 1844 in Christchurch workhouse, Surrey. Her age is given as 30, and husband William BOWLER (hatter).
In 1851, I have William BOWLER in Southwark, Surrey with occupation of 'slate polisher' and birthplace Denton, Lancs. He is married to Mary c1805 from Mayo, Ireland. Ref HO107/1564 377 8.
I have the marriage cert for William BOWLER & Mary Ann BRETT in 1845, Parish of Christ Church. William gives his occupation as general dealer, and his father as Nathaniel BOWLER also general dealer. Mary (spinster) gives her father as Richard BRETT.
In 1861, I have William BOWLER again in Southwark, with occupation of 'school slate maker' and birthplace Lancs. He is now married to Elizabeth c1811 from Deptford in Kent. He has 2 stepsons, Edmund FOX and Alfred FOX, with him. Ref RG9/331 128 25.
I found a marriage for William BOWLER and Eliza FOX in 1858 in the Parish of St John, Waterloo, Surrey. William's occupation in the certificate is 'school slate maker', but this time his father is George BOWLER (hatter). Eliza's father is Benjamin HILL.
By the way, this William BOWLER is not to be confused with the one who went on to make the first Bowler Hat

, although I believe they are related.
So....are these William's all the same person? If they are, why did he give his father two different names? The only suitable death I can find for Mary BRETT/BOWLER is 1859 Q1 in Southwark, three months
after William married Eliza...I need to send for it. I haven't found a death for William yet (there's one in 1864, Christ Church, but this isn't him).
Would burial records be the way to go now? What else can I do to tie this up, or get more clues? Sorry for the length of my post, but I'd be grateful for any help or pointers!!!
Thanks for reading,
Helena
