Just been checking how often my male ancestors were marrying the sisters of their dead wives. Not uncommon in my family particularly in the 1800s in UK and OZ.
Seems logical to me .... am imagining ... if I am younger sister, living at home with mum and dad, my older married sister dies leaving husband and children. Mum says "right we have to help out. You, cocksie, are to go over and help with the children - poor old hubby "John" has to work and there are nappies to be changed. Off you go, cocksie". I don't have a car (or horse) and it is easier to stay at my brother-in-law's house as he has an early start and someone has to be there to look after the children. This goes on for a couple of months, all relatively comfortable, am helping brother-in-law grieve, keeping house & children in order, cooking, washing ........ couple of hugs turn into a couple of kisses, turn into ....... next logical step is a piece of paper!
cocksie