You can make them the Active Person & then use the [[Gramps_{{Version manual}}_Wiki_Manual_-_Tools#Relationship_Calculator|Relationship calculator]]via the {{man menu|Tools->Utilities->Relationship Calculator.  This tool is interesting because it lists the relationship conversationally. That is, it says something like "Smith, John is the great grand uncle of Weaver, Susan. Their common ancestors are Smith, Mark and Carpenter, Mary}} menu." 

However, the Relationship Calculator can also be overwhelming because it lumps all the Relatives of the Active Person into an a large alphabetical list. So, you'll have to find a Person by name instead moving through a pedigree the relationships via connections in the Tree. If the Tree is too big to keep a Pedigree snapshot in your head, you're in for some navigation awkwardness pain. You'll have to cross-reference the people you find in the Views while navigating the Tree in the List of the Relationship Calculator.

 You may might find it is more natural to assume your conversational subject will revolve around one person. You can put Gramps on the same conversational footing.