This may or may not work, but it's worth a try... Before calling out the sibling on negative behavior, try some positive reinforcement with the younger son. If you give the positive reinforcement first, it may settle his mind that he has gotten his attention first for being good, then try to deal with the other in a time out. In your hypothetical example of the dinner fork you could try something like "Johnny you are a good boy for eating your vegetables, I like it when you do that!", Then deal with the fork stabber (you might have to take her fork while speaking to the brother to save your table top) by placing her in time out in the next room. Stay with the son for several minutes before going to speak with the sibling. This lets both children know that to get your attention first, they should use good behavior. With very young children 5 minutes is an eternity, those few minutes of rewarding good behavior with positive attention will probably be more effective than grounding them for a week. Kids tend to forget why they are being punished if the time out lasts too long.
If you and DH can double team the brood it's even better, one deals with the transgressor while the other does something fun (small is is fine, maybe tell a "knock knock joke" or something) with the kids who have been good it will be much more effective. Be sure to let young children return to the family as soon as their behavior calms down. This lets them know again that you love them and want them to return to the fold when they can behave. If you have to go into extended management of a more serious behavior problem, try and do it in private, and be sure to do something nice for the other kids like giving them a game to play or an occasional cookie so they don't feel like they are not getting any attention while you deal with the problem child.
Kids who demand negative attention are most likely just demanding attention period. Some are thrill seekers though and enjoy the drama. The best thing you can do either way is limit the drama. It can be it's own reward, or be construed as attention. Both set a bad precedent and encourage misbehavior.
Hope this helps!