@kiranc13433869
If you are drag & dropping a component(which has child/nested parsys in it) into layout container responsive grid of editable templates then all the components which are allowed in that particular layout container policies at editable template level are by default allowed to add in that child/nested parsys inside that particular component.
/content/page/jcr:content/root/ - layout container root (say you have allowed 'x' component group or 'y' components by editing template or through code by defining policies under /conf/project/settings/wcm/policies/wcm/foundation/components/responsivegrid/policy_34324324 & map this to policy as value to cq:policy property under /conf/project/settings/wcm/templates/content-page/policies/jcr:content/root)
Drag & drop component A
/content/page/jcr:content/root/componentA/ - component A
Component A has parsys in it say 'new_par'
/content/page/jcr:content/root/componentA/new_par - this parsys new_par by default inherited/enabled with 'x' component group or 'y' components which allowed in parent layout container responsive grid.
to answer your query we can set this allowed component policies through code or by editing templates as well.