"These people eat ducks."
Translation:Ci ludzie jedzą kaczki.
You are close. But it's not "a group of male persons", it's "a group with at least one male person". Even if it's 999 women and one man, it's still grammatically masculine personal. Other than that, you are right. And as "people" have at least one man (otherwise you'd say "women", after all), it's masculine personal.