I can share my (very limited) experience. I made what is basically Prison Hooch after watching a YT video, where the guy put a cup of sugar into each one litre juice bottle. I had 2 litre bottles of juice, so I put two cups in, which after a lot of shaking still left perhaps a centimetre of undissolved sugar at the bottom of several bottles. It wasn't a problem, once fermentation started it all dissolved over the course of the next day. So my assumption is that the yeast will take care of it.