CC'd to your own e-address in case I make a mistake in preparing this for the Forum...
My immediate reaction is to try to work back in both families to look for a join. To do that I'd look at [a] census records, [b] BMD indexes [c] National Archive database (esp. for naturalisations) [d] London Gazette archives [e] Jewish Chronicle archives. At some point you'd need to get official certificates, to make sure that you aren't following a false lead. I'd recommend buying certs direct >from GRO or the local registration office, direct (ca £9), rather than through any agent (usually charging a very substantial premium).
I had a look for the DIAMOND family: -
Abraham DIAMOND appears with his family in the 1911 census. You can glean quite
a lot >from what is available for free - especially if you take info >from one
access-site to another. Alternatively, you can gain access by pay-as-you-go
credits on a couple of sites, or by a subscription. That would give you access
to the original images.
His marriage to Phoebe STONE, in the Cardiff registration district in the
September quarter of 1909, shows on FreeBMD. Your only problem is to know
whether yours is Abraham DIAMOND or Abraham *David* DIAMOND - both of whom appear
on the same registration page. A certificate, requiring Phoebe STONE as the
bride would make sure you had the correct one.
Adele's birth record can also be found in FreeBMD - so long as you allow for
an unexpected spelling of "Adelle", as can that of Beatrice (1916) and Cicy/Cissie
(1914), showing mmn = STONE.
Googling shows that there's also a sefardies.org website which shows this family,
but my browser seems to be picking up unlikely name- & date-combinations (children
born long before the parents' marriages; children with different surnames >from
their father's). However, some of its detail looks likely - a specific marriage
date falling in right year/quarter in the right place. That site gives Abraham's
father as "Harris DIAMOND" (possibly >from the marriage certificate, given that
they have given a specific date for the marriage). A marriage cert would give
father's name and occupation... or what the bride/groom *claimed* was the father's
name and occupation. It is not unknown for certified information (name, age,
occupation) to have been "enhanced" for one reason or another (social advantage,
avoidance of embarrassment, getting round the law).
The London Gazette archive picks up a 1923 naturalisation for an Abraham DIAMOND,
who is a draper in Cardiff, so likely to be "yours". You *might* be able to get a
copy of the official documentation >from The National Archives at Kew. This could
give you some useful genealogical information. The fact that it's less than 100
years ago makes it more problematic.
There are death notices in the Jewish Chronicle for both Abraham and Phoebe.
I have access only to the tempter-snippet that is available publicly, but you may
be able to get access to the original articles - again they could give you useful
genealogical information. I rather think that there are other family notices for
them there, but I don't have enough access to be sure. I think that there may
also be notices for other Abraham DIAMONDs - including another one in the Cardiff
area - so you'll need to be discerning in what you pick out.
Incidentally, for many people (like me!) it really does help if you show
surnames in upper case: they leap out of the blocks of prose, and also make it
easier to distinguish between given names and family names in cases where the
family name may be the same as a given name (e.g. DAVID) or vice versa.
SW Herts, UK