In case the succession was semi-salic the heiress would be princess Milena as the daughter of prince Boris assuming he outlives his father.
The current succession in both Montenegro and Albania is salic. So no rights to succeed to or through the female line.
In both cases i could see that altered if no male heir is born. In Montenegro it's unlikely. Prince Nicholas is a widower but at an age i don't see him marrying again and starting a second family and prince Boris and his wife have been married for a long time. Princess Veronique is 46 years old and their daughter Milena was born in 2008. There has been some debate about them having a second daughter Antonia but i've never seen any official statement that the couple had a second daughter outside one picture.
Like Romania they could opt to alter the line of succession to gender neutral. In that case Milena and Geraldine would become the heiresses in their countries.
In Italy it seems Vittorio Emanuele and his son Philiberto Emanuele seem to have done the same thing but they have a junior male line in the Aosta branch and for the Two Sicilies the Duke of Castro has done the same for his claim that is however already disputed by the duke of Calabria.
It's rather easy to change succession rules in an existing monarchy. The Parliament can pass a law, and that's it. But in a former monarchy, you can always have claimants stating that the old rules should be abided. Italy and The Two Sicilies are excellent examples of this.