He spoils and defends her.

Will is sitting in a box on the kitchen floor and eating a bag of ‘pop tart bites’ as Nic and I unpack the Costco run. Ellie is harrassing Will, shrieking for more of his pop tart bites, which Will is handing to her.
Nic (sternly, walking over to intervene): Ellie, NO. That isn’t the way to ask for things.
Will (handing Ellie more pop tart bites): It’s okay. She can ask naughty.
When Ellie was assigned to this family, she sure did luck out. There has surely never been a more patient and loving big brother!