Looking for the names, birthdates , parents etc.etc. of gr.gr.gr.grandparents

John Thomas b. 1774 married Elizabeth Martyn (born 1778) on 3rd August 1799.

Also John Edwards b. 1783. d.1864 married Jane (or Jennifer) Corin b. 1784 d.1846, on 19th January 1805. What were their parents' names??? Any help appreciated. Could possibly be from St Erth and Gulval.respectively.