Did you already tried the constrained by function? See documentation here: https://docs.mendix.com/howto40/constrained-by-functionality-for-a-reference-set-selector
Regards,
Ronald
In this scenario it is key to refresh the entity (caller-of-the-page/dataview) once you have selected the value in the first reference selector.
This On Change refresh microflow which you should add to the on change event of the first reference selector, should refresh the caller of the page/dataview entity and will trigger the datasource microflow for the second reference selector.