Could these be brothers?
As yet the paucity of relevant records means we know very little about James Owen's siblings. However, it is interesting to note that there were other Owens in Shrewsbury in 1851 who may well have been related to James. From the evidence of the first marriage of James's daughter, Isabel, which took place at Trinity Church, about half a mile from Coleham (now a suburb of Shrewsbury) it seems likely that James had a family connection with a John Owen of Coleham. The witnesses of the marriage were John's son, Samuel, and John's son-in-law, Charles. Further, John had been born in about 1792 in Llandrinio, a village neighbouring Llandysilio, which was where Isabel and her mother were born and very close to James's place of birth; James was born in about 1806 in Llansantffraid and educated at Deythur (now Deuddwr) all less than 4 miles from Llandrinio (map 1). Further, I am told that John's father was also called Thomas, all of which strongly suggests that James and John might have been brothers.
There are descendants of John Owen who believe that John's parents appear on the 1841 census, living in Collfryn (see again the detailed map). Note that in the 1841 census the ages of adults were rounded either to the nearest 5 or to the nearest 10 years. The people in the Collfryn household were Thomas Owen (70), a gardener, Ann Owen (70), David Owen (40), a farmer, Catherine Owen (40), Ann Owen (13), David Owen (14), James Owen (8) and David Brees (16), a taylor. All, apart from the older Ann, were born in Montgomeryshire. (The next census entry on the page is for a household in Deythur indicating how close the two communities were.) It may be a coincidence but it is interesting to note that one of David Owen's children was called James.
Thus James may have been the brother of John and/or David.