Isinglass and chitosan are finings. Might be included in wine kits but as a pack of finings rather than in the main ingredient container, you could sub Bentonite, which is basically clay.
Gelatine is sometimes added to improve mouthfeel. Dunno how likely it is to be in a kit.
I'd be surprised if this hasn't been asked before (though I don't recall seeing it myself) so a search for, say, "vegetarian" on here or "vegetarian homebrew" on Google will likely turn up some good info. The Vegetarian Society (I assume they're still going) may have some info. The kit makers certainly will.