Best advice I can give is try the original recipe and see how you like it. For us it was to acidic/sour. More sugar and all it did was make it too sweet and still acidic.
The 2nd batch I only used 2 bottles, not quite as acidic. Then I made an f-pack of 7 pounds of 4 berries I bought at WalMart. Have not really tasted it because we have a few half gallons/quarts in the fridge we are working on. The 4 berry has a gorgeous red/blue color. More of the blueberry/blackberry color then the strawberry, red raspberry color. We do plan to sample it soon.
I am starting a 3rd batch, hopefully today and plan to cut it back to one bottle of lemon juice and use the slurry from the 4 berry pee.
Will it work? I have no idea but it is a worth a try.
I am a long time cook/baker. I cook from scratch, not a box mix person. Even after 43 years of marriage, I still make a main meal every day for just the 2 of us.
I always use the original recipe and then make changes to fit our tastes. So, it was only my natural instinct to make changes to suit our taste. And in this case, get the acid content down.