Jane, its been some delay since you posted your message but hopefully you will receive it.
I am researching my family history and came across your posts on William Mustard.
Do you have any information on a James Mustard b 18 Feb 1832 in Sunderland (?Williams brother). He died 18 Aug 1907 in West Hartlepool and married Charlotte Cairns 21 Sept 1850. Their daughter was Ester Mustard b 5 Oct 1928 (my great grandmother).
If you can provide any information and I possibly may have more I can give you depending on if its the right family I would love to hear from you.