I have two younger non identical twin sisters. When my mum was pregnant she was told they were both in different sacs when developing but shared the same placenta.
We have done hours of research on the topic, as we have reason to believe they could after all actually be identical.
After all this research we’ve just found a load of fancy names for twins and no information on non identical twins that share the same placenta and are in different sacs.
Another thing that may help is that they are mirror twins.