As a double gunner myself, I love the idea of duel flintlock. Believe me I do! But the problem is that it would be EXTREMELY hard to balance correctly; either it will be broken and way to powerful, or it will be useless and not powerful enough.
Lets look at the options: According to the OP, the flintlock when duel wielded would have be less accurate and have a damage of 30 per bullet, and you can only care those two flintlocks. This would be a completely worthless load out, since it would basically be a nerfed version of an eye of reach WITH NO BACK Up WEAPON.
Secondly, the option could be to keep the same duel wield scenario of the original post, but you could carry a third weapon. This of course, would be over or under powered depending on the weapon you choose. If you choose a sword as a secondary, it would still be a worthless load out, since you could just use an EoR and sword combo. If you choose another gun as a secondary, it would be overpowered since you basically get a 10% increase in damage then the current sniper pistol combo.
Thirdly, the option could be to keep the duel firearm damage and bullet spread, but increase the amount of bullets you get in a load out to 12-15. However, this would still make the load out worthless, because why would I use 4 bullets to kill a pirate when i only need 2?
Therefore, I propose a fourth option. The only way duel flintlocks would work in the current combat system would be to make it so it would be 45% per bullet; of course, this would also be hipfired shots. This would make it so it is not a one shot kill, but you also have a reason to use it over the EoR. You would not be able to carry another weapon, and you would not have any more than 10 bullets. Also, it would take twice as long to reload as a flintlock because you would have to reload both of them. Honestly, even if it was like this I don't know if I would choose it over an EoR and pistol combo. Because, like I said, why would I choose to kill someone with 3 bullets when I only need two?