Hello Elaine. I'm glad to have helped.
I've tried to find "Aunt Margaret Russell" but no luck. There were no Margaret Russell's born IOM anywhere in England in the 1851 census as far as I could tell. There was a younger one in Liverpool in 1861 but that's all. I did a family search using all the surnames of parents and grandparents to see if one married a "Russell" but nothing came up. There were about a dozen ladies named "Margaret" born IOM in 1851 in Yorkshire. One was in Huddersfield, which is close to where Willemina Gelling married. She was Margaret Barker age 25 and her husband was Richard. This couple married in Douglas in 1849 and her surname was Clark. There's a younger sister Isabell E Clark age 20 born Douglas with them in Huddersfield. No obvious connection here.
When Willemina married in 1848, she was very much underage. Her marriage in the June quarter 1848 is less than 16 years after her baptism of 14 Nov 1832 at St. Mathews Douglas, though she might have been baptized a bit late (she was 10 [listed by her middle name Margaret] in 1841). Perhaps she eloped? Her step-mother Mary had died 2 years before in 1846 and her father Edward didn't marry wife #3 until 1850.
Benjamin and Willemina's 2nd child was Thomas Edward, and he was 8 months old in 1851 census, born Clayton West, Yorks. His birth and death are on the FreeBMD indexes. He died 1852 before they emigrated, so that's why you didn't know about him.
It would appear that the mother Jane Cannell was bp 16 Jan 1799 St Mathews and she'd be one of 13 children on IGI of Robert CANNELL and Elinor CANNON m 21 Jan 1792 Braddan. Jane's burial is on the IOMFHS Burial index 4 Dec 1832 age 33. The stepmother Mary (Brown) was buried 28 Jul 1846 St George Douglas. Edward Gelling was buried 15 Dec 1856 Braddan. His widow Elinor Ann (Milbourne) lived on to 1907 age 92.
My email is egelling at shaw dot ca.
I hope I answered all your questions.