In the book, as the women give birth, Gary lets the monsters into the house and he then escapes. Everyone (includingTom) is killed and Malorie gets a call inviting her to the community minutes after giving birth and her entire group being killed. She decides to raise the kids first - not as a mother - but as a trainer, ensuring they are equipped for the eventual journey. She trains them for 4 years and employs some questionable tactics, like hitting the babies if they woke up with their eyes open and refusing to feed them until their eyes were closed. Basically she trains the kids to listen, not see, and forces them to do that for her all along the river.
In the book it’s strongly implied that if you were mad, you weren’t driven to suicide. Gary is mad and actually camps outside the house for weeks watching the group from his tent. The monsters effected animals too, driving a dog to self mutilation and making the birds along the river at the very end kill each other too.
The river stuff... time scales aren’t given in the book as she sails down the river. Malorie is also attacked by a wolf when the accidentally row into the side of the river and passes out for a bit, leaving the kids to do the rowing. She’s confronted by a monster at the end that tries to remove her blindfold, but she refuses to open her eyes. In the books, the monsters don’t whisper or impersonate lost ones.