A William Savill was baptised in South Ockendon on 10 June 1798. His parents were William & Elizabeth Savill.
South Ockendon & Aveley (Where John Savill was baptised) are in the same registration district, so it is likely that this is John's brother.
A William Saveill married a Jane Mills on 25 December 1823 in Orsett.
The 1851 census for Farm Road, Orsett shows the following :-
William Savill, aged 54 an agricultural labourer who was born in South Ockendon
Jane his wife aged 52 who was born in Launceston, Cornwall
Martha his daughter aged 13 who was born in Orsett
George his son aged 11 who was born in Orsett
The 1861 Orsett census shows
William Savill aged 61 a labourer born in South Ockendon
Mary Ann his wife aged 50 who was born in Orsett.
If this is him then Jane nee Mills died and he remarried.
In 1871 - Conways, Orsett
William Savill aged 72, labourer born Southend (South Ockendon)
Mary Ann wife aged 60 born Orsett
The 1881 census shows a William Savill living "Near Pound Gate, Orsett", an agricultural labourer aged 82 who was born in South Ockendon. He was living with his wife, Mary Ann aged 70 who was born in Orsett.
William was buried in Orsett on 3 May 1883 aged 85.