I'm very sorry for the slow reply, we've been away in the UK. Thank you for your message and congratulations on managing to navigate your way through all those Gellings! All that information is extremely helpful, I had gone off on a wrong tangent after John Gelling's (abt 1800-1875) parents so I'm very happy to be on the right track once more and I can't wait to share this information with the rest of my family.
Yes, Rosemary Derbyshire (née Gelling) is my mother and her father is Robert Christopher Gelling (Chris), John William Gelling's son.
As you are a Gelling yourself - are we related?!
Thank you so much, again.