For "Read to a child for two hours," you can read to any child--it doesn't have to be your sim's child.
The only time I was ever able to complete Tier IV of this aspiration was during a Baby Boomer Challenge.
Every other time, even when my sim's child maxed an aspiration, "Have a child max an aspiration" milestone wouldn't complete. That was just my personal experience on three occasions, though.
Also, if your sim adopts a child, the game considers it the child of the adopting sim, but not the child of the adopting sim's spouse.
Someone with more experience can answer your other questions.
Good luck!