This would be a commment but it is too long for that.
Is it even possible for a habitable planet to have a year 6.78 times as long as an Earth year?
At twice the distance from a light source the light will be one quarter as bright. If the two stars are equal in luminosity, the combined light from both of them will equal the light level from one of them when a planet is 1.4142 times as far away as it would be from only one of the stars.
Thus if the two stars have equal luminosity, the inner and outer edges of their combined circumstellar habitable zone will be only 1.4142 times as large as the inner and outer edges of the circumstellar habitable zone around only one of those stars.
In our solar system Mars has a year 1.88 Earth years long and Jupiter has a year 11.86 Earth years long. The asteroid Ceres has a year 4.61 Earth years long.
So a planet orbiting our Sun with a year 6.78 Earth years long would orbit somewhere between the orbits of Ceres and Jupiter. And it would be far too cold to have liquid water on its surface with an atmosphere breathable for beings similar to humans. If it had a more exotic type of atmosphere with a lot more greenhouse gases, it might be warm enough for Earth type lifeforms, but then the atmosphere would almost certainly be unbreathable for large multicelled land animals such as the natives are probably supposed to be.
If each of the two stars in your system are much more luminous than the Sun, a planet at that distance could be warm enough for Earth type life. But each of the two stars should be more massive than than the sun of they are more luminous, so their combined gravitational force on the planet should be much stronger than that of the Sun on a planet at that distance. Thus the planet would have a faster orbital speed and it would take it much less than 6.78 Earth years to complet one orbit.
And a writer can keep adjusting the masses and luminosities of the two stars until he finds a realistic, naturally occuring mass/luminosity that produces an orbital period of 6.78 Earth years somewhere in the systems combined circumstellar habitable zone.
Known exoplanets have orbital periods ranging from a few hours to hundreds of thousands of years. Since the habitable zones of stars are much narrower than the range between the closest and farthest possible planetary orbits, the range in oribital periods of planets in the habitable zones of stars is much smaller, but could still include orbital periods of tens or maybe hundreds of years.
Except that stars luminous enough to have their habitable zones wide enough to include orbits that wide and long probably cannot shine with a steady luminosity long enough for their planets to become habitable for beings similar to humans.
The best scientific discussion of the requirements for planets habitable for human beings, and thus for aliens with similar environmental requirements, is Habitable Planets for Man, Stephen H. Dole, 1964, 2007.
Dole explains that it took billions of years for Earth to acquire an oxygen rich atmosphere and become habitable for beings who breath oxygen. Dole also explains that the most massive and luminous stars remain on the main sequence and shine with reasonably steady luminosity for periods shorter than the billions of years necessary for a planet orbiting them to become habitable.
According to Dole's calculations, it should be impossible for a star more massive and luminous than an spectral class F2 star to have a habitable planet. It would also have to be luminosity class V instead of a more luminous, giant type of star.
So you need to find the mass and luminosity of spectral type F2V stars and calculate the inner and outer edges of their habital zones. Then mulitply by 1.4142 since your system is a binary. Then calculate the orbital periods of planets orbiting at the inner and outer edges of the combined circumstellar habitable zones from the distances and from the combined masses of the stars. If a planet oriting at the outer edge of the combined circumstellar habitable zone of a double F2V system would have an orbital period of less than 6.78 Earth years, then it would be almost totally impossible for any habitable planet anywhere to have a year as long as 6.78 Earth years.
One way out that would be to make the two stars more luminous than F2V stars, pushing their combined habitable zone out far enough for a plent in it to have a year 6.78 Earth years long. That would make the stars too short lived for the planet to become habitable naturally, so it would have to have been terraformed and given an oxygen rich atmosphere by an advanced civilization sometime in its plast.
Another way out would be to make the system a double double system. It would have four F2V stars in two pairs. Each pair might obit each other at a distance of about 2 million miles, nearly touching, and the two pairs would orbit each other at about five times that distance, or ten million miles. In such a system the inner and outer edges of the combined circumstellar habitable zone would be twice as wide as the zone around a single F2V star.
Another way out would be be to go to the PlanetPlanet blog and The Ultimate Solar system section, devoted to designing solar systems with the highest possible number of habitable planets.
Some of those solar systems are so statistically improbable to occur naturally that they would have to have been constructed by advanced civilizations.
And some of the most far out examples there may have set ups where habitable planets could have years as long as 6.78 Earth years or longer.
One way to have a habitable planet with a year 6.78 Earth years long is to have it orbit outside the circumstellar habitable of its star so that it would be too cold for life except that it has a major source of heat additional to the heat from the star.
One way to do that would be to use tidal heading from tidal ineteractions with other objects in its solar system.
Such an process is discussed in my answer dated 12-17-2020 to this question: