I am not looking at the Coward tree - and other than looking at original certificates - I take many online trees with a pinch of salt

I am sure that your mother is quite right that John Young didn't marry Mary Prescott

I am saying that Mary Prescott married 1) Joshua Lyons in 1846 and 2) James Atherton in 1850
and that she is the mother of Betty Lysons born 1848.
Betty Lysons/License then marries John Young in 1872 (after having Joshua Lysons in 1870)
It would be interesting to see what info you have about this marriage when you get back to your computer..
Milly
Betty Lysons birth
DecQ 1848 Wigan 21 738
Joshua Lysons birth
Decq 1870 Wigan 8c 77
Betty Lysons (License) and John Young Marriage
Jun Q 1872 Wigan 8c 26