If you are thinking the baptisms were at the Baptist Church in Sible Hedingham, then they will have been adult baptisms (or "believers" baptism) made when a person is old enough to have made their own decision to believe. Baptsit Churches do not practice baptism of babies too young to have made their own decisions on what they believe.
Records for the Baptist Church will not be under Parish Records - those will only be records for the Parish Church - which will be a C of E Church.
If you are sure your ancestors worshipped at the Baptist Church, it might be worth you contacting them to see if they have any surviving archives.
http://www.hedinghambaptist.org.uk/However - if they were christened in the PArish Church, I see the online registers on the SEAX site do not go late enough for the dates you mention.
The records will be at the Essex record office (closed this week , opens again on Monday)
Where did George Heesler and Susannah Hale marry? Was that at the Baptist Church? What age does he give on marriage cert?