It´s a pleasure for me to help with what I know.
About the last question, according to the myth, Osiris is killed by his brother Seth and later is resurrected by the magic of his sister / wife Isis, who conceives a son with him: Horus.
Osiris is the first mortal god and that brings him closer to humans, to common people. However, he can only be alive in the Realm of the Dead, he will no longer be able to return to the land of livings. He becomes a benevolent god who welcomes the deceased into the afterlife.
In the Egyptian concept, life on the hereafter is a reflection of life on earth of livings. On the other side, deads must continue working cultivating the fields of Osiris. The Egyptian gods do not dictate norms to humans, it´s humans who says how the gods live and interact.
The dead can sometimes return to the land of livings and visit their relatives and see their home, but only for a short time.
My theory is that this is related to the rise of religious beliefs. I understand that ancestor worship existed first, as a way to keep the social group together and preserve the memory of learning.