Pauline,
I'm a descendant of Thomas Karran and Anne Ratcliffe, and live in Highland, Utah. My email address is phil@karren.com.
Just this evening I spent 4 hours at the LDS Salt Lake City Family History Library, looking through Onchan parish records: baptism, marriage, death, confirmations. I found multiple Thomas Karrans, as well as lots of other Karrans. I still have to piece what I collected together.
I did see that Thomas was born in May, 1810, born to a Thomas Karran. However, the entry didn't mention the mother.
Family records indicate that Thomas' father is Thomas, born in 1782 in Onchan parish. I can confirm that there's a birth record for this Thomas as well.
To complicate matters, possibly, there are also many Thomas Karrans in Braddan parish, and family records indicate that Thomas Karran (b 1752) and Isabel Kewley had a son named Thomas. I looked a couple weeks ago at Braddan records, and indeed found this Thomas.
There's some dispute from there as to who the parents are, and I'm trying to sort out what the truth is.
If your'e interested, I'll drop you a report when I get it all together.