one site, old posts by man and late wife, new posts by man, want new to include old and new, old inc

One site. Husband and wife posted for years. Wife passed away. Husband continues posting on his own after wife passes. Goal: can click on a link to 'husband and wife posts' and see only posts by hubby and wife. Goal: Main blog contains newest posts and goes all the way back including all the new husband and all the old husband and wife posts. Currently the old posts are in a separate wordpress install/domain. How do I do this? Thanks in advance for your reply.