I don't think what they call lemonade is as sweet as 7-Up, do you? I force-carbonate lemonade and use that. It makes a pretty good match for the Radlers I've had in Munich.Shandies are generally not brewed, Leinenkugel notwithstanding. Shandies are usually mixed in a serving glass by adding beer to lemonade.
I've not brewed with huckelberries before. If they are like blueberries you will need at least 1 lb/gallon for a huckelberry beer.
And traditionally, it's a soda like 7 Up. It's referred to as lemonade in other countries.