Did it kinda easier........
To your left is a small bump in the wall of Tommy's office. I stood there to avoid fire. The mafia guys half to walk all the way around to shoot you so your good with cover fire. While going for the bastard Lance......pop your head out and run to the opposite balcony of Lance to your left when you exit the office. Give him a Rocket Sandwich to avoid him form leaving.
*note-this sometimes may not work....I don't understand it but the first time I tried it.....Lance never made it to the roof and th 2nd time.......he got up and ran anyways.......
Go back to the safe and use that wall for cover for awhile. Then when its time for Sonny..walk to the the steps and release either a gernade or smoke bomb-the one you find at the cops precinct at Ocean Beach
This should take care of the bodygaurds while you pop Sonny a good one
And hey Sleazy-thats a pretty crazy technique and approach to the mission. Guess we all have our styles