I visited your link and it seems to me that the cards *are* responsive, inasmuch as when I resize the browser they take up the available width in 3 columns and below a certain width they stack on top of each other in a single column.
You are using Bootstrap columns for this in your View output.
Is there something different you mean by responsive?
When you create a View to display cards in this way you specify the number of columns, and it looks like in the View you linked to 3 columns were specified.
Because of how Bootstrap (which Toolset uses for its grid system) uses rows for its grid and how Views generates the markup, you must decide when creating the View how many columns to use, and if you need the same results elsewhere with a different number of columns then you'll need to create separate Views for each.
So edit the View and run the Loop Wizard to design the output and specify 2 columns. If you are using this View somewhere else where 3 columns are required then duplicate the View and edit the copy to change the number of columns.
