I was just about to post this when I realised that on one them Mary signs her name (as Mary Ann) and on the other she makes her mark, which is what she did on her marriage. Now I'm wondering if there are two Thomas and Marys about but I've been over the baptisms and they all look OK. I was always confident that Mary Susanna was their child as Thomas' mother's name was Susanna.
Mary witnesses a few of her children's marriages - Mary Susanna 1836
http://search.ancestry.co.uk/iexec?h...c=&pid=6411166
Maria 1832
http://search.ancestry.co.uk/iexec?h...c=&pid=6400662