Of 27 John Gellings born between 1790 and 1810 only one was christened in K German.
July 20 1806 to James Gelling and Sophia Lamothe:
John Dominique Gelling.
Sophia is on Brian Lawson's site as being buried in German on December 24 1844 age 76. I can find her in the 1841 census in Santan aged 72 with children John 35 and Catherine 27, but not James.
Also on Brian's site is the transcription of the will of Dominique Lamothe, Sophia's father, in which she is mentionned.
It would be nice if it were the same one