Bottled grape juice

So. My parents have plenty of grape vines and every year they bottle some of them using a juicer. They literally have a hundred of these bottles around quart sized. Couple questions. If I attempt to make wine out of these. What sort of concentration do you imagine I'll need (they are juiced with a steam juicer and they often mix with a packet of koolaid for a one gallon mix). And anything special I should look for? Tannin concentration? Adding fermentables? Etc. it's going to be an experiment. The grapes they have haven't been properly tended so end up kind of middle sized and there is a combo of purple and green ones (don't know the varieties). It's one of those things I've been wondering about. Was going to get around to doing something with their two pear and three apple trees this year but got busy. Anyway. Any suggestions would be awesome.

I get a lil anxious when you say there's koolaid mixed in. lol

You need to take an SG reading, pH and TA (total acidity).
Koolaid is very acidic. You might have to adjust the "juice" for pH or TA or both.

Adjust the SG to where you want it for final alcohol %.

Koolaid also contains other things like salt, citric acid, acorbic acid and sometimes preservatives like BHA.
Yeast definitely does not like salt. BHA is an antioxidant, so not sure how that would affect.

I would say use a yeast like Lalvin K1-V1116 made into a starter.

Even better, get ahold of some without the koolaid by doing some harvesting there yourself.

Actually the bottles are the straight juice. The koolaid comes when they mix it to drink it (1 qt grape juice + 1 packet of koolaid and some sugar and water make a gallon of decent tasting juice). So that's not a problem. I'm just worried about the properties of the juice. Does it lose anything from the juicing process? Worry about stuff like that etc.

Oh yes I might mention. They have a ton of these straight juice bottles. Grapes go in top. Steam. The. Juice comes out bottom. Bottled. Capped and stored. So it's basically the same as getting from the garden and a great deal fresher without preservatives than say welches (which I've seen people make).