Start with high-confidence family conflict resolution books, then narrow by subgenre or adjacent topics.
The Love Prescription
John Gottman PhD, Julie Schwartz Gottman PhD
Fault Lines
Karl Pillemer Ph.D., Karl Pillemer
Eight Dates
John Gottman Ph.D., Julie Schwartz Gottman PhD
Wired for Love
Stan Tatkin PsyD MFT, Harville Hendrix PhD
How to Untie a Balloon
Ryan Dunlap, Kwame Christian