Mafia romance by Sable Voss
Crime family power, treaties and succession. The couple is still the A-plot.
6 Sable Voss books do this. Each one has its whole first chapter free to read, so you can tell in ten minutes whether it is the version of the trope you want.
Vow of Ruin
A Dark Mafia Romance
Not yet for sale
A Devil's Mercy
A Dark Mafia Romance
Not yet for sale
Blood Oath
An MM Dark Mafia Romance
Not yet for sale
Crown of Scars
A Dark Mafia Romance
Not yet for sale
The Saint We Buried
A Dark Mafia Romance
Not yet for sale
Empire of Thorns
A Dark Mafia Romance
Not yet for sale