In your story The Potter Alliance, Sirius should banish Draco and Narcissa from house Black just to p*** off Lucius and Voldylocks. Plus, another idea is when Walburga (Siriuss mother) took control of house black and spent most of the Black fortune to Voldylocks and Malfoy. Because she had no authority to spend any of the Black fortune without the head of the houses permission, and Lucius gladly took it. What would happen if there was a law that if a head of house took money from another house without the Lord's permission. That head of house *Cough* *Cough* Ferret boy senior, aka Lucius Malfoy, will be required by law to pay the money back.
Again this is just a suggestion.