Good question, in the story of Moe's relatives, Donand and Daisy disguise themselves as duck relatives. As for the question about Firmina, it was published there, as well as Aracuan with Paperetta Yè-Yè in "A Turma da Pata Lee", however, the Italians did not create stories with these interactions (although they use Fetrhy as Red Bat and your nephew Biquinho).
In B 950008, Cousin Chachá Tinho says that cousin Zaroia Pernacurta (something like Cross-eyed short leg) wants to marry Moe, Moe mentions Tia Catira, who would be a Headless Mule.