Many thanks for this, Frances. It helps clear up some of the muddle because Ann Gelling als Gelling's will of 1733 doesn't provide her husband's name. Now I learn that the two parents of the couple in the 1726 contract were engaged to each other! Aha!
Given the date 20 Jul 1726, I can see why it was important to get these two children married "within a month" as their first child Margaret was already on the way. It is interesting too that the bride, Catherine Kelly, was actually a widow. She had married William Corrin in 1724, but he died 10 months later, but fathered their child Catharine (she md John Fayle 1850 - issue). Ultimately she did well by John Gelling of Camlork with 9 more children, and buried together in the Braddan church having both lived into their 80s (see Braddan MI's in Manx Notebook).
I haven't seen either of the Paul Gelling decrees (1736 and 1760). That's on my future list.
You're correct in the last paragraph about the other Paul Gelling & Ann Kelly couple, who married 1729/30 Braddan. They each had wills, 1783 and 1770 respectively. I think this Paul will be the one baptized 15 Aug 1703 Braddan son of Patrick Gelling & Margaret Kelly (formerly wife of Wm Kinnish, and then after Patrick G died 1708 became wife of Daniel Cain).
Your suggestion that the two key marriages here would likely be in Marown is a good one, given she was of Ballavargher Marown. And those marriages are missing, right?