This is what worked for me...
Create a form (call it SelectDates) and put 2 unbound text boxes on it. Call them txtStart and txtEnd. Then go to each of your queries and put the following as the criteria for your date fields:
BETWEEN Forms![SelectDates]![txtStart] AND Forms![SelectDates]![txtEnd].
Next put a Command button on your form to run your report. In the report put 2 unbound text boxes where you want the dates to appear. I usually put them in the report header. In the first box, I make the DataSource; =Forms![SelectDates]![txtStart] set the label to "From". In the second box I make the DataSource; =Forms![SelectDates]![txtEnd] and make the label "To".
Now, when you open that form, you enter the dates just once and each query pulls the dates from the form and they show up on the report.