You could try this but you will not be able to adjust the figures with doing it this way.
Select both figures and clothing and “Export” as OBJ
“Import” this OBJ back into Daz Studio
set collison as the two figures are now one object..
Yes, that works as well. Just to add, set resolution of the figures and clothing to base in parameters tab - mesh resolution, before you export to reduce amount of polygons (geometry) you dont need.