I only had a problem with the two ships together, to be very honest, but I never really followed a guide to do it. Which I’m guessing is the problem with your approach, you need to play to your own strengths/play style.

My strategy for them, if it’s going to help you out, was kiting. Hit it with the mortar from as far as possible and try to ram it if they get close, brace as much as possible but don’t stay defending for a long time as they’ll gain on you. I noticed that they tend to stay on the defense and try to stay away when you make enough damage. After utilizing the two weapons above, swivel guns and chain shots when able and of course the heavy shots were great to add extra damage before getting away.