Yumi and Takeshi are Hana's children. Hana is Keiko's sister, making Yumi and Takeshi the niece and nephew of Keiko. Since Akira and Satoshi are Keiko's children, this would make Yumi and Takeshi their first cousins. 

Considering Kenji is also described as Hana's son and Keiko is his aunt, Kenji could be either Yumi or Takeshi, depending on their respective genders which have not been specified. If Kenji is a male, then he would be the same person as Takeshi, given that both are described as the son of Hana. If Kenji is a different individual, it would indicate an inconsistency in the information provided, as there can be only one son, according to the initial description stating Hana has two children, Yumi and Takeshi.
Akira is Satoshi's brother. Their mother, Keiko, has one sister named Hana who has two children: Yumi and Takeshi. How are Yumi and Takeshi related to Akira and Satoshi? Given that Keiko is the aunt of Kenji (Hana's son), is it possible that Kenji is either Yumi or Takeshi? Respond very briefly.