I’ve begun taking a closer look at this family which I have to admit I haven’t previously researched beyond Thomas and his relationships to my own lines.
It looks to me as though his parents (and therefore those of Margaret) were William Darley and Mary Grayson. The reason you may have been having some difficulty tracing them is that they appear to have been Roman Catholics and the records are in non conformist record sets. I’ve found several more siblings and will begin entering details over the next few days. It would be great to work together on this so please feel free to contact me directly.