I still can't beat the final form of father gascione. Came so close but his attacks are super fast and little room to maneuver.
Are you:
-using the music box (can be used three times)?
-maxing oil urns and Molotovs?
-taking advantage of the central headstone ring and the larger crypt in the back for the final form?
-using visceral attacks?
What weapon did you choose?
I did most of my damage on the final form of Father G with oil urns followed by molotovs because I wasn't very skilled at that point in the game.
Protip: When not locked onto and enemy, extend whatever weapon you chose with L1, and master the rolling attack. Circle... (half second pause)... R1 and then circle again. You will come out of the roll swinging and then jump right back into the roll.
Obviously this all depends on the enemy's attack combos, but in general, when I'm at a difficult enemy and have to stay mobile, I usually do 2 rolls. The first roll when the enemy begins an attack, and the second to get behind them. I come out of the second roll attacking with R1. From there you can choose to follow up attack or roll. I usually roll.
Two things to consider with this strat: since you are not locked on, you will need to aim your attack coming out of the roll with the left analog stick. Practice this in empty space so you know your stamina limits very well. You should always know how many rolls, combo attacks, etc you can complete at your current stamina level.
The holy sword is good for big and slow mobs.
I leveled it up to +5 or 8 and it was pretty underwhelming. The broadsword is *OK* if you get yourself in a bind and need crowd control on a bunch of weak characters, but the kirkhammer does so much more single enemy damage and is much more deadly in combo attacks with roll. I totally regretted putting blood stones into the holy sword at all.