I continue to think there's two or more chaps named Christopher DONNELLY in rural/regional NSW in the 1870s ... which takes me to the NSW BDM online index, marriage 1867, Queanbeyan, Mary MCDONALD and Christopher DONNELLY... #2932. Without ALL the info available from the parish register re the bride and the groom and their parents it is simply NOT possible to consider that Christopher is the same chap who married Mary MAKIN...
I don't see how it can be considered a bigamous marriage.
Re Mary MAKIN marrying twice .... and then having a child by her first husband several years after her second marriage....
Sorry, but dots are not joining up for me. It is of course up to you to set your own standards of proof for your own research.
JM