Thanks Jim - and all other contributors. The relationships are much clearer to me now. The only great-grandmother with a living husband for photo 2 would be Mary Thomas (1838-1921), though she looks remarkably young for a 60-yo in photo 1.
Alternatively, is it possible that photo 2 shows the union of two families - one related to the man in front and the other related to his wife in front? If the man is on the side of his own family (say) then family 1 is represented by him, his mother, and her 16-18yo grandson. Family 2 is represented by the wife in front, her 2 big sisters at the back, and her father. The two girls (if both are daughters of the couple in front) are with their aunt and maternal grandfather.
In that event, the grandmother and grandfather would not be married - but may both be widowed. This would make the younger two great-grandmothers (1844 and 1848) credible candidates for photo 1. It is consistent with your take except that the lad would not be son of one of the sisters. If you think this plausible then I'll try to identify the participants in this scenario too.
