Using a date slicer with existing date filters on visualizations

I have a set of 12 visualizations on a page which show the last 13 months of rolling data. The relative date filter is set on the visualizations.

This works well but I now have an additional requirement to have a date slicer on the page which allow the user to select a custom timeframe.

I would normally set a page level filter for the slicer but a mandatory requirement is that the 13 month period must show initially. (The slicer will automatically go to the oldest date in the data )

So the report needs to show the 13 month period initially, then change to show whatever the user enters after that.

(Also, if the user selects a time prior to the 13 month period the charts won’t show that data because of the visualization filter. )

What would be the best way to handle this?

Thanks.