As per my understanding you wanted a make provision to show and select two dates.
With the dates you wanted control all the functionalities of the current and other blended data sources.
If I'm right, I would prefer to create two date parameters called Start date (30-sep-18) and End Date (31-dec-22)
E.G. End Date sample parameter
With two parameters you can control all datasources in tableau workbook.
Hope this helps! Plz mark the response as helpful and answered if it solved the problem