Configure Islandora Entities (Islandora -> Solution pack config -> Islandora Entities) and find "Solr base query for citations"
Here you can modify the query to include other content models. For example, to include both the Citation and Large Image content models, use:
+RELS_EXT_hasModel_uri_mt:("ir:citationCModel" || "islandora:sp_large_image_cmodel")
The parallel bars ("||") are the OR operator. You can add as many as you need to in order to include all the necessary content models in your search.
A list of core Islandora content models and their PIDs can be found at https://github.com/Islandora/islandora/wiki/Content-Models. For content models that come from contributed modules (such as Islandora Remote Media), see their Github repositories for the identifier.
Note that you will need to include the person’s identifier in the metadata for these other objects in the same way you include them for Citation objects.