To do this you will need to find out the kill condition for five made men. To do this you will have to go around the streets looking for people with a key above there head. Once you have located these people you must speak to them using
twice during the conversation to accept the favour. You can then use
to bring up the map and locate the favour's location, use
to get the details of the favour, then head over there and do what the description tells you to do.
After completing this favour go back to the start menu and press
to access the don's menu, select the opposing family and find out how to kill them and where, then head over to the target and kill him in the condition you have been told. Repeat this five times. If you do not want to do the favour use THIS GUIDE
to find out how and where to kill the made men.