Ok, as a Vet of over a dozen invasions on Test and over a dozen more on Open, here is a few of my two farthings worth:
On all the enemy voodoo users (Witchdoctors, Gypsies, AND Jolly) use Hex shot and/or thrown daggers to break their attunement and decrease their voodoo. This can be a switch back and forth between weapons. I have done this numerous times when I see I am taking damage from spells and can see the undead who is doing it to me. I have also done it to help my fellow pirates under attack in the same way.
Using Hex shot on Jolly (once he is at the Mansion especially) helps decrease his voodoo attacks.
If there are high level pirates using staff, help protect them.
High level pirates using staff: Keep track of the battle and move to areas under heavy attack to use your staff to help your fellow pirates.
Cover each other as much as possible, even if you are not in the same crew.
Keep track of the red dots on your compass. Especially those outside your barricade area. This helps you know when to fallback to defend another area, especially the Mansion.
If the barricade you are defending does fall, that is a sign you should immediately withdraw to the Mansion and defend from there.
Remember -- it is the Mansion that must be saved in the long run.
Have fun!
