I have only just joined, hence why I'm so late to the party!
I hope this may be of use although it may not be directly connected to the original post re Sidney King. I have been doing my King family history on and off for years. Because many of them were Independent's they only pop up as marriages in the established church, the other records are a bit sketchy. I am hoping also that someone might be able to shed some light on things that might help me get further back.
Robert King (bac) married Mary Baker (sp) both of this parish at Melbourn on 14th Oct 1788. In 1805 on 6 Jan at Melbourn PC a number of Kings were baptised as being of Robert and Mary. They were John (b 16/6/1790), Lydia (b 12/11/1792), Elizabeth (b 4/9/1794), James (b 23/4/1796), Ann (b 4/3/1798), and Joseph (b 2/3/1800). On the same day and date Ellis (b 8/11/1804) was also baptised but as being of Robert and Elizabeth.
My theory is that Mary must have died some time after the birth of Joseph. Robert then married Elizabeth and they had all the step children baptised at the same time as her first born. I have not been able to find a burial of Mary nor a marriage of Robert and Elizabeth. Would the church have baptised children born out of wedlock? Robert and Elizabeth went on to have other children that were also baptised at Melbourn PC - William (b 15/4/1806), Susanna (b 21/5/1808), and Sarah (b 24/3/1810). In 1817 at Melbourn Independent chapel, Frederick was also baptised as being of Robert and Elizabeth. On the 1841 census there is a David who would have been born approx 1812, who I also believe to be a son of Robert and Elizabeth.
Robert King died 5 Jan 1837 aged 72, and is buried at Melbourn Independent chapel, so he would have been born approx 1765. Elizabeth died in 1848 aged 66. She is described on the death certificate as relict of Robert King ( Baker). It would seem that Elizabeth was Robert's junior by 17 years. Also in the Independent chapel in 1823 on the 22/2 and the 20/3, as well as 1824 1/8, a child of Robert was buried.
Going back to the OP...
Robert and Elizabeth's son Frederick (bac) was married to Elizabeth Barker (sp) at Fowlmere PC in 1848. Frederick (Carpenter/Baker) died 11/11/1868 aged 52 and was buried in the Melbourn Independent chapel on 16/11/1868.
1871 census
13 Melbourn High St
Elizabeth age 48 widow born Fowlmere
Frederick son age 18
Albert son age 16
Elizabeth dau age14
Ann dau age 12
Walter son age 10
Robert son age 5
In 1874 at Melbourn PC
Frederick King, full age (bac) carpenter, son of Frederick (carpenter) married Amy Jane Louisa Pryor, full (sp) dau of Alfred (Publican). This Frederick was born approx 1853 so an educated guess says he is the brother of Sidney. Frederick died 4/1/1893 aged 40 and is buried at the Independent chapel with his wife Amy, who died in 1883 aged 34 yrs. There is also a burial of Albert King aged 3, son of Frederick, in 1853 (he was 1 on the 1851 census) so it would seem that Frederick senior and Elizabeth named their next son Albert after the first one's death.
With the other suggestions that the name Baker might be Barker, I'm now wondering if Roberts wife Mary was infact a Barker, could it be that further down a generation that Roberts son by Elizabeth may of married into the same Baker/Barker family.......something to mull over?