you will need to reference your input variables in your charts measures to effect the dashboard. Using a bit of set analysis in the expression to set your condition on dates between vStartDate and vEndDate.
Without looking at your solution I think you would need to include the date range constraint in your measure expression. I've not used qWidget date picker before so am unaware of the specifics of how it works (I couldnt find it in Qlik Branch) but I assume the date picked gets stored in a variable. you just need to include in your measure expression on the charts that need to use it.
If you have applied this last minute then you will need to go through all your charts unless you have stored your measures as master items in which case you can modify that and it will update all the charts that use it.