I think you've gotten some great advice.
1) Get the girls spayed as soon as possible. You can search for low-cost clinics at http://www.pets911.com
(if you're in the US).
2) Separate at least the kitty being picked on, though I like the idea of reintroductions altogether.
3) More litter boxes. If the family's up for it, I would go for five of them. More litter boxes helps diffuse territorial issues. The rule of thumb is you should have as many litterboxes as you have cats plus one. Some of us don't have the space for it, but if you do, go for it.
4) I'm not sure I read it on here yet - but invest in FELIWAY. This is a synthetic hormone that mimics the "friendly" markers in cats' cheeks and helps calm down a multicat household. Do not spray it near litter boxes or scratching posts/places.
5) Buy Bach's Rescue Remedy (Flower Essences). Whoever cleans their water dish(es) every day should add a few drops to it/them. Dab ALL of the cats with it behind their ears, at the base of their tail, and a good large dab under the chin - this one will waft up into the nose. It doesn't always work, but when it does, it works.
Here is a link for explanations on the flower essences and Feliway - I'm sure you can find both cheaper: http://www.catfaeries.com
6) Buy a black light - like this: http://www.ambericawest.com/blacklight.html
Use it after dark (turn off the lights) to go through the house and find all the pee places. They show up as orange in the black light.
7) ...and buy an enzyme cleaner to clean up the pee. We've tried the Urine B Gone and didn't have much luck with it. We've tried most of them, in fact, and though this is a little pricier, it is VERY effective: http://www.nokout.com/odorelim/pets/
If I were you, I'd order the 2 1/2 gallon jug - or at least one spray bottle and a gallon. An enzyme cleaner is what you need to remove the scent of cat pee TO THE CATS. This is so important in helping to stop the inappropriate peeing cycle I can't tell you. And you MUST let it air dry. What we do is after COMPLETELY soaking the pee area with the enzyme cleaner, blot it up after 10 or 15 minutes, and then we put aluminum foil over the area and just let it air dry. If it's bad, it may need a second application.
8) If you can afford it, buy either Cat Attract litter to use for a month or two - if not, buy the additive and add it to the existing litter. This is a good price for the additive: http://www.entirelypets.com/catattract.html
9) Talk to the fam about vertical space. This can also go a long way to resolving territory issues. Buy cat trees or create a pyramid out of those storage boxes - cut holes in them so the cats can go inbetween and up through them - or do this with sturdy cardboard boxes (what cat doesn't love a box? We built large 3D "castle mazes" using a lot of duct tape and scissors.....) - buy boards for shelves, L brackets, and create stuff like this: http://www.katwallks.com/customerphotos.htm
As to the music - it is not just classical music that helps. It is calm classical music that helps, specifically harp music! Here are specific music suggestions:http://www.musicmypet.com/http://www.catfaeries.com/music-for-cats.html
Do the cats get fed any meals? Or do they only free feed? If they get fed meals, feed the alpha up on a table or counter.
Do not try to discipline the cats for peeing outside the litter box. They aren't doing anything wrong - they're letting you know they've got stress issues.
Have someone in the family play with the alpha kitty for at least 10 - 15 minutes every day, and give her lots of extra love and attention.
With the little picked on kitty separated from the group, focus on getting the peeing problem under control, let everyone (including your family!) de-stress, give them vertical space to help with the territory/alpha problems, then work on re-introducing the picked on kitty using positive reinforcement.
When it comes to reintroducing her, add vanilla to the mix. Yes, continue the rescue remedy, but do the exact same thing with natural vanilla extract (available at health food stores - don't buy the normal synthetic supermarket stuff). This will help confuse the smells, and should help the reintroduction process go more smoothly.
Good luck, and thank you for wanting to help your kitties be happy.