"At the beginning go to the clothing shop and buy a new suit. Now you can go to the Winston's wedding.
Behind the door gangsters are waiting for you. Defeat them and then get rid of thugs on the ground floor.
A moment further you find another door, and behind them an armed man. Grapple him and take his pistol. It'll be useful to eliminate remaining thugs.
At the end of the rooms you find a dying Winston. Talk with him and move on.
When you get on the upper floor of the main hall, kill the enemies above firstly. Then you can pick up their weapons and eliminate those on the ground floor.
After the firing ends, round the room and go downstairs. Uncle Po is waiting behind the door.
You have to take this man to the hospital. Green points on the map show the way.
When you run into enemies, look for the high cover (unfortunately you can't use L1). Leaning out from behind it, you can kill enemies without risking Uncle Po's life. After getting to the hospital the mission ends.