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Recent records can be harder than older ones because many have 100 year closure rules.
The Jersey Archive website has indexes of births, marriages and deaths but you will need a subscription to view them. It's not too dear, about £35 per year which includes unlimited downloads but as you are looking for recent records it might be an idea to browse the catalogue first - https://catalogue.jerseyheritage.org/collection/Search/advanced/archive/

Jersey certificates are eye-wateringly expensive, over £30 each and double that if you don't have a reference, which you get from the Archive indexes.

The Jersey Family History Society can do research on your behalf, they charge £15 per hour

Mary Ann Prescott married J J Alger at St Saviour's church on 20 Oct 1864. He was born in Devon and she was born in Weymouth and was the daughter of John Richard Prescott.
On 2 Oct 1884 Mary Ann, widow of J J Alger, married William Charles Le Brun, he was 10 years her junior and by 1891 William is shown as being a widower.

According to the funeral director's record he was buried in St Brelade new cemetery in Grave 133 however he died in St Helier. The death is indexed in St Helier Vol 64 and is on page 32.

I'd be a bit doubtful about the 1826 baptism that you found in Islington for Susannah Caroline.
From the 1841 census the inference is that Susan, William and Cecilia are siblings of Caroline which makes it a mystery why Robert and Margaret would name 2 daughters Susan, unless the baptism is actually that of Caroline's sister. Did you notice that a Robert Cooper of the same parents was baptised on the same day?

Going back to Thomas Hamon -he was born in about 1816 and was the son of Thomas Hamon and Susanne Rachel Ereaux who married on 9 Mar 1815. However Thomas Snr must have died pretty soon after the marriage as Susanne married Elie Coutanche on 9 May 1820.

There was only one birth actually registered as a child of Thomas Hamon and Caroline Cooper and that was Thomas Alfred Charles in 1842/3 however there are 2 baptisms. The first was Thomas A C baptised in St Helier on 22 Feb 1843 and the other was Charles Thomas also in St Helier on 24 Dec 1848. The godmother of Charles Thomas was Susanne Rachel Ereaux. I imagine he was the 3 month old Thomas shown on the passenger list for the Typhis which arrived in New York in May 1849.

The Hamon-Ereaux-Cooper connection is further strengthened by the fact that William Cooper is living with Elie and Susanne Coutanche on the 1851 census.

Their funeral services were held at St Mark's Church but as it does not have a burial ground they are buried in Mont a l'Abbe cemetery. Other MacFarlings in the same grave are William 4/2/1933. Ann 8/1/1911, Charles F 12/2/1949 and Lydia Florence 27/7/1995.