Ravelin, out of interest, in the original image of John HARLOW and Mary SMALL's marriage on FindMyPast, there is a marriage above it. One of the witnesses for yours was John FORD and above is the marriage of John FORD to Mary HARLOW, in which John HARLOW was a witness

I'd be disinclined to pay any attention to Family Search family trees, as with any other family tree site. They can be made up of total rubbish.
As for the two Ash Mary's, there is a suspicious burial in 1741 in Ash for a Mary Small... makes one wonder, but no indication which child if either.
The christenings themselves give no other info. My next thought would be to check out other children of the couples to see if any sibling names lend themselves to Mary Small's children.
Samuel and Mary nee NASH (m. 1732):
James 1733
(Mary 1734)
Elizabeth 1736
Samuel 1738
Sarah 1741
Joseph and Mary nee WOODRUFF (m. 1727):
Daniel 1729
Joseph 1731
(Mary 1734)
John 1738
Sarah 1740
Do any of these names appear in John and Mary's children?
I wouldn't be surprised if Joseph and Samuel were brothers though.