Hi Colin
Griffess' death certificate lists his mother as Elizabeth Ashdown. As mentioned elsewhere in this blog, Elizabeth Ashdown married William Tree in 1792 in Woodchurch, Tenterden, Kent. This is very close to Northiam, so I think it's highly likely that these were the parents of Griffess Tree(s). By the time Griffess was born in 1808 the couple had 6 children. I have not been able to find a baptism for Griffess, but can think of numerous scenarios for the omission. William died in 1812 and could have been ill for some time, making it difficult for Elizabeth to organise a baptism for Griffess being one possibility.
Tracking down Elizabeth King's parents I found a bit trickier. I had quite some help for this from TimAussie, who I think you have also tried to contact. FamilySearch lists a baptism for Elizabeth King son of James and 'Mary' King in Rye, 24 Feb 1811. Tim had gone through the films at an LDS library and thought the 'Mary' was a mistake, and that it should have been Sarah. Looking at the children on James and Sarah it fits, particularly as the witnesses to the marriage of Griffess and Elizabeth were Daniel Tree, Maria King, Martha King, Mary Tree and Frederick King. James and Sarah had daughters Maria and Mary, and James had a brother Frederick who was nearly 20 years his junior.
Elizabeth King's brother, James Kelsey King, also came out to Australia, in 1939, and died in Sydney in 1893.
I tried to contact TimAussie some time ago without success. He may have changed his email address or just stopped researching. Would be interested to know if you have any response from him.
Regards
Judy