When I looked I found most of my marriage records for Wambrook were before 1874 like your family mine left Wambrook.
I assume Elizabeths parents were Thomas & Hannah and she was Bapt 7.10.1849 Chardstock.
Can you list the sibling you are interested in if there marriages took place after 1874 I probably do not have them.
I also have connections in S. Petherton. I expect you have accessed the S. Petherton website.
Sorry I cannot help more at present
