I suggest you to try creating extract and use Tableau Data extract command line utility to refresh your extract data in Tableau desktop.
Please read the article below for how to do this.
Let us know if you were successful.
It is very easy to get it done.
1) Create a Tableau dashboard by connecting it to any database connection
2) Save the dashboard as .twb file (not .twbx) it will also save the .tde file along with this dashboard
3) create multiple copies of the same dashboard (.twb) file and let them all refer to the previous .tde file
Now whenever you will refresh the data of .tde file through any of the dashboard (in desktop version) all other dashboards will also get this refreshed data. In The tableau online version you just have to refresh the .tde file and automatically all the linked dashboards will take refreshed data.
In your case (when you have already created dashboards) save all of them as .twb files and delete all the .tde files saved along with them but one. when you will open the dashboards it will ask for .tde file at that time point all dashboards to that same .tde file
Hope this helps.