"I'm helping her realize her feelings. I'm tired of listening to her nonsense about Aaron." That is one of Josh's reasons for sending Nathalia to go after Aaron. He is tired of listening to Nathalia's mouth.
Every time they talk about the twins, the first name that comes out of her mouth is Aaron's name. Before it was all about Anna, now, it's all about how annoying Aaron is, how Aaron can easily attract other ladies and all sorts of topics that Nathalia could say about Aaron.
To those who are close to Nathalia, can tell that she thinks of Aaron more than just a friend. She doesn't even realize it herself, and that is what annoys Josh because he has to watch and hear everything from Nathalia.