Looks to me like Mary & Susannah are the same person
1871 - Dukinfield
John Jarvis 63 - coal miner b Tinsley
Susannah Jarvis 58 - b Chester
Amelia Jarvis 19 - b North Leigh
May [Mary] Jarvis 12 - b Tinsley
RG10, 4081, 68, 4
1861 - Tyldesley
John Jervies 50 - coal miner b Tyldesley
Susanna Jervies 43 - b waverdon, Wales [possibly Waverton just outside Chester?]
Alice Jervies 11 - b Hindley Green
Amelia Jervies 9 - b West Leigh
Susanna Jervies 3 - b Tyldesley
RG 9, 2907, 45, 11