URL Pattern in node entity reference
I suppose you use D7?
Do you use the Inline Entity Form module to add a new referenced node of type B? (https://www.drupal.org/project/inline_entity_form). I just tested the following workflow with the Inline Entity Form and Pathauto, and path aliases were successfully created for both nodes (type A and referenced type B):


enable inline_entity_form and pathauto modules
create the Entity Reference field on content type A that references content type B; select 'Inline entity form - Single value' as a widget type
create patterns for both content types in admin/config/search/path/patterns (ex: for A - 'news/[node:title]'; for B - 'people/[node:title]')
create a new node of type A, within it create a node of type B
both nodes should have the correct aliases