The real question is, what leads up to the bite, what are they doing the parrot doesn't like? If he doesn't like them, why is he in such close proximity to the people he will bite? Does he fly to them and attack, or are they coming to him? If he is taken to them, that needs to stop until he's better trained. If he's flying to them to attack them perhaps it's better for everyone if his wings are clipped until he's trained. I can't believe I'm saying that, I hate wing clipping. But if he goes to them to bite-that may be the only option. But if someone he doesn't like is forcing themselves on him, then the people are the problem and the bird should not be clipped. This is fixable if you're willing to train him. One thing I noticed with the people in my house who didn't get close to my conure is that because he didn't like them-it led to teasing by them of the bird while in his cage. He would try to attack them through the cage and they thought it was funny so they'd sort of bait him by sticking their fingers through the bars to tease him.
As soon as I realized they were doing that I put a firm and fast stop to that with a good snarly "mom lecture". It went something like this: "Anyone messing with the bird when he clearly doesn't want them to has to stop. You have to respect his personal space and not force anything he doesn't want on him. Would you want someone you didn't like or trust grabbing at you or forcing you do something you don't feel comfortable with? If you want to build a relationship with him and have him like you, you must be gentle, don't tease, offer treats, move slow and be kind. Eventually when he's ready he'll let you touch him. If he's not ready, don't force him. If you can't deal with him patiently then just leave him alone. And if you don't you'll have me to deal with." Harsh? Maybe, but I don't want bleeding people fingers and unhappy neurotic birds who feel threatened in their own homes. That leads to rehoming of birds which is bad for everyone when they could have all gotten along well with the proper training and had a great pet who loved and trusted them. Now they offer treats and move slowly so he doesn't get scared of them. They talk to him through the bars instead of poke at him. Slow, steady, patience, being gentle and calm wins trust in the end. And food, lots and lots of treat rewards.
There are some great training videos on the market. Ebay is full of "Good Bird" training dvds by Barbara Heidenreich. There are books as well, like the Parrot Wizard's Guide to Well Behaved Parrots. Look up Santina Rescue bird on youtube and you'll see a variety of videos by that guy on how he tamed a rescued Macaw who needed a lot of work and who bit.