While Family Guy has done several Star Wars parodies, including a whole episode titled "Blue Harvest" that spoofed "A New Hope," a dedicated prequel trilogy hasn't been announced.
It's possible that such a project could be considered in the future, but it's important to note that:
* Licensing: Using Star Wars characters and elements requires approval from Disney, the current owner of the franchise.
* Production: Such a project would be a major undertaking and would require significant resources and time.
So, while it's not impossible, it's unlikely that a Family Guy Star Wars prequel trilogy is in the works right now. But, who knows what the future holds for these beloved franchises?