Good answers on the technical question already. I'm just writing to say that even if you make a wine with no sulfites added added, that wine is still very likely to contain naturally occurring sulfites. So if your friends are truly allergic or at least sensitive to sulfites it still may not be the best idea for them to drink your wine; and you should not call if sufite free, but instead say 'no sulfites added but some occur naturally in wine.'
But you also said that a number of friends are sensitive to sulfites, and I feel like folks often attribute things like sensitivity to sulfites, when in fact they may not be sensitive to sulfites at all. They may instead be sensitive to alcohol, or sensitive to tannins (which are similar to histamines), or phenolic flavonoids. Basically scientists say that only about 1% of people are truly sensitive to sulfites, but because this 1% is truly allergic to sulfites we see warning labels about sulfites and now everyone attributes things like 'red wine headaches' to sulfites which are likely not the culprit. Good read on the topic here:
The science behind those painful wine headaches
You could draw a parallel between sulfites and gluten. Only a few people are truly gluten intolerant but many more people try to avoid gluten for a variety or reasons (some more sound than others).