Joey had marred a rather conniving woman named Dina. Although Colin didn’t attend their wedding, he had met her briefly.
Colin knew she didn’t love Joey by the way she looked at him, and assumed it was the house she was after.
In a year, Joey contacted Miranda wanting to buy House 5. He offered slightly more than half of its value.
Colin was going to argue when he heard the price. Then a few bits of reality rained.
Obviously Joey didn’t know about the Will. He was going to buy something he would get for free in a few years; that is half free, for he would have to share the house with his brother Keith.
If Miranda sold it to Joey, Keith automatically lost his half of house 5.
Then Colin realised it wasn’t being sold to Joey alone, but Joey and Dina; meaning that she would kick him to the pavement and take the house.
This would result in both Keith and Joey losing House 5.
And that loss pleased Colin in a childish way.