Now that we know that Shisui is indeed Kagami's son, we can talk about a family tree.
First family:
I believe that Kagami is Madara's son. This would show how he inherited the Will of Fire that Madara seemed to have when he was younger. It would add to the irony of him also gaining his beliefs from his father's rival. I also think that Obito is Kagami's first son, and Shisui's older brother. This would explain why he wanted his sharingan (for EMS), and how he was able to use a similar genjutsu to control Yagura.
Second family:
I used to believe that Fugaku was Izuna's son, making Sasuke and Itachi Izuna's grandchildren. This would explain how the Susano'o can stay in the bloodline, and why Sasuke looks similar to Izuna. However, the only fault in this is that Izuna seemed to die in his 20s and is unlikely to have had any children.
Madara ----------- Izuna
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Kagami Fugaku
| |
Obito -- Shisui Itachi -- Sasuke
The only other possibility I can think of is if Fugaku is also Madara's son, which would explain why he became the head of the clan after Madara, and how the clan could have survived if Izuna died before he had children. Due to the whole importance of bloodlines and ancestors, I think we can guarantee that Obito, Shisui, Itachi and Sasuke are direct descendants of Tajima Uchiha.
First family:
I believe that Kagami is Madara's son. This would show how he inherited the Will of Fire that Madara seemed to have when he was younger. It would add to the irony of him also gaining his beliefs from his father's rival. I also think that Obito is Kagami's first son, and Shisui's older brother. This would explain why he wanted his sharingan (for EMS), and how he was able to use a similar genjutsu to control Yagura.
Second family:
I used to believe that Fugaku was Izuna's son, making Sasuke and Itachi Izuna's grandchildren. This would explain how the Susano'o can stay in the bloodline, and why Sasuke looks similar to Izuna. However, the only fault in this is that Izuna seemed to die in his 20s and is unlikely to have had any children.
Madara ----------- Izuna
| |
Kagami Fugaku
| |
Obito -- Shisui Itachi -- Sasuke
The only other possibility I can think of is if Fugaku is also Madara's son, which would explain why he became the head of the clan after Madara, and how the clan could have survived if Izuna died before he had children. Due to the whole importance of bloodlines and ancestors, I think we can guarantee that Obito, Shisui, Itachi and Sasuke are direct descendants of Tajima Uchiha.