First I'd start with management, stress reduction, relaxation and treating the whole dog.
More details here: http://pets.groups.yahoo.com/
Then I'd work on some training/obedience. Decide what you want the dogs to do instead of what you don't want.
Sit when visitors arrive? Run to Mat? Run to crate? Grab a toy, etc.. Teach the desired behavior during relaxed times when no visitors are there.
Then I'd work on visitors with one dog at a time. Starting with someone that they know and like - roommate, spouse, best friend etc..
You can use techniques from Grisha's Stewart's Behavior Adjustment Training or Leslie McDevitt's "Control Unleashed"
Or just plain ol counter conditioning - starting with one dog at a time and staying below threshold.
Teach what you what you want the dog to do as the visitor arrives (after you've taught it alone)
After each dog is performing well separately with known people, then you can put them together.
When you are ready to work with less known visitors, separate the dogs and start from the beginning. For unknown folks it is probably best to start outdoors - far away enough from the person so that dog becomes comfortable. Once the dogs are comfortable outdoors (could take days, weeks or months), then bring that person indoors. Have the person walk in, then the dog. Ask the dog for the behavior you desire while the visitor does absolutely nothing.
If that goes well, you can start acclimating the dog to visitor movements
visitor lifts a pinky, YOU toss a treat
visitor raises hand (arms still), You toss a treat
visitor raise arm, you toss treat
visitor pretends he is about to get up but doesn't, you toss treat
and so on.
Do this with one person at a time, one dog at a time. Until each dog is comfortable. Then put the two dogs together
You might have to back this up even further by just acclimating the dogs to knocks and doorbells.
While you are doing this, keep visitors to an absolute minimum. Meet friends at their place or a coffee shop or something. If you must have scary visitors before you have acclimated them to visitors, teach them how to relax in a room by themselves. When visitors are due to arrive, have them call so you have time to calmly put the dogs away. Tell visitors to not ring the doorbell or knock. Just calmly let them in while the dogs are put away.
More on visitors
Be sure that You always give treats and not the visitors