The Preferred family is normally used for graphing and pedigree analysis.
Also, see Main parents family in Gramps
This is the topmost family in the Relationships view. (Parent and Spouse)
The order of Familes (both the Parent and Spouse families) can be changed in the Relationships view for the Active Person. The order of Spouse Familes can be ordered in the Edit Person dialog for that person. Re-ordering is an important and complex aspect of Gramps relationships.
Some analysis recognizes multiple relationship paths… but that is more on an exception than a rule.