MAYNARD from Kent England

My brick wall is my 3 x grandfather, Charles Maynard Born ~1804c, 1841 and 1851 census have him down as born in Leigh. At some point before 1833 he married Martha Lee (can't find registration for this either), Martha born in Seal, Kent, to parents Jonathona Lee and Martha Lee nee Mitchell. Charles and Martha had seven children, Eliza, William, Mary Ann, Thomas, Elizabeth, Esther , and Charles, all born in Sevenoaks, Kent. Another researcher has a George Maynard marrying a Jane Lee in Sevenoaks with witness's Charles and Martha Maynard. This is the only possible other relative i have for Charles. Maybe brothers married sisters?, but no proof. i have tried to find parents for Geroge Maynard and tried to tie Charles in that way, with no sucess. Charles and Martha, along with 5 of their children migrated to Australia as assisted migrants in 1852 aboard "Helen", one child ( Charles) died enroute. They were sponsered by William McIntosh and Duncan Mc Rae of Mosquito Plains South Australia. I am very keen to find a birth, christening, marriage, anything about Charles Maynard's life in Sevenoaks, Kent, England. And of course his wife Martha Maynard nee Lee. Anything that anyone can suggest will be most welcome, even if it sounds obvious to you, i may not have tried it, and am happy to sift through info that i may or maynot have seen before.