I have dss (8), dsd (7), dd (7), ds (4) and dd (2). Dsc mother has always been discouraging on them sharing their belongings (we've been together for over 5 yrs) - when they were younger they'd hit and tantrum over it. Now they just refuse and can be quite mean to my dc, particularly dsd. She expects that her belongings will remain untouched by my dc both when she is here and when she is not, yet she expects to be able to play with anything she fancies that belong to my dc though she often breaks/loses things/doesn't ask first/doesn't put things away etc.
My dd(7) is from my previous marriage and dsd expects to be able to play with all her things when she's at her dad's, so it isn't like dsd has the sole right to be upset that another child could be playing with her things when she isn't there. I don't know how to deal with this. My three tend to share well so there's no 'house rule' regarding it, as such. I'm torn between saying if dsd won't share her things then I'll be telling dd not to share with her either as it's only fair if everyone's sharing. Or else that all toys are to be shared fairly and are of no belonging to any one person in particular, but to the family.
Aibu to ask what you would/do do in this situation?