I asked LRO for a copy of the marriage of Thomas Marston and Mary Kilby but they did not marry in Leics . So no luck with the witness search. I have one last idea if someone would be kind enough to help me. That is to find a death for Catherine Marston nee Prole in Queniborough before 1783 to see if she was a first wife of William. I will be so grateful for this information.