Hi
Unfortunately Henry died in 1839, and there isn't a birth for him on the IGI, these are their wedding details Henry aged 22+ and Mary Lines 21+ at time of Marriage, Walsingham District, Morston Marriages (Parish Register) 1817 putting them around 1793/94 ish not found their births and parents for clues which doesn't really help I know. Hannah could be a sibling of Henry's or a sis in law, there is a problem I've heard with rounding up and down with the 1841 Census, I've seen it happen with other families in my tree and Pete's.
Julie