Overall I thought this was a great chapter. These insights we are getting into the shinobi world before the formation of villages and countries shows how brutal and savage Hashirama and Madara had it. As to itama, I agree that Tobimara was most likely experimenting with edo tensei with hopes of bringing back his brother. It is also important to take note of what Tobimara said was important "Shinobis should repress their feelings" I believe that a lifetime of suppressing his emotions caused Tobimara to create edo tensei in a desperate attempt to get his brother back...
Pertaining to Madara, I too was surprised by the fact that he had 4 brothers. However, I believe that these brothers must have been older and had little to no bonds with Madara, thus causing him to care little when talking about their death. Izuna on the other hand we know grows up with Madara, making their bond deeper and when Izuna dies it causes Madara to go insane. The 3 brothers that Madara lost serve only to show that short/menial friendships mean nothing to Uchiha, it is the deep bonds that cause them to lose sight of everything and go crazy