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how do you teach the Lv. 4 Limit breaks to all of the characters

thats pritty much it...

Barret(Catastrophe): If you saved North Corel from the train, a lady in the second level...thing of huts will give it to you.

Vincent(Chaos): You either need a Green, Black, or Gold Chocobo, or the Sub. The waterfall is a circle of water near Nibelheim. Get off the Sub or Chocobo near the grassy part and just walk into the waterfall. If you're on Disk 2, you'll only get a cutscene. If you're on Disk 3, you'll get a cutscene, and then (I think) you're prompted to leave the cave. Go back inside, and walk up to where Lucrecia was standing.

Yuffie(All Creation): Finish her Pagoda sidequest

Red XIII(Cosmo Memory): You win this from defeating Lost Number inside the Shinra Mansion in Nibelheim.

Cid(Highwind): In the Cargo Room on the Gelnika

Tifa(Final Heaven): On the third disk, go back to Nibelheim with Tifa in your party and go in Tifa's house. Go upstairs, and opt to play the piano. Press the following buttons: X, Square, Triangle, R1+Triangle, R1+Square, X, Square, Triangle, R1+X, O, X, Square, X.
You should get it, and a letter from Zangan that explains a lot.

Aerith(Great Gospel): This is a bit of a tricky one. Once you have the buggy, drive it into (literally) Costa del Sol. Pay 100 gil to the guy standing by the boat that took you to the new continent a little while ago, and he'll stash you onboard. You'll end up in Junon. Head out, either by using the helicopter or elevator, and ride your buggy across the little river, over to the cave entrance. You'll come upon a sleeping old man. Talk to him, and if the number of battles you've fought (or, so I've heard, the number of times you've escaped) is a 3-digit number whose last 2 digits are the same and odd, he'll give you mithril. If they're even, he'll give you a Bolt Ring. Once you have the mithril go back to Junon (paying 10 gil to ride up the elevator), and get back to the second continent. Now, once you've gotten to the part where you're trying to find the Keystone, go to the Gongaga weaponsmith (at the tip of the peninsula near Gongaga) and talk to him. You can go ahead and ask him about the Keystone. Once you've done that, choose to change the subject. He'll ask for mithril, you give it to him, and then he'll ask you to choose a big or small box. The big box is downstairs near the bed, and opening it will get you a Gold Armlet; nice armor, but not the one we want. Go up the stairs and you'll find a small box on the wall. Open it to get Great Gospel. Please note that you can only choose one of the boxes, and once you've opened one, you can't change your choice.

I think that's all of them...as has been said, Cait Sith only has 2 limit breaks, so I didn't include him. Sorry this turned out to be such long post sweatdrop I do hope it helps you.

EDIT: EEP! Forgot Cloud, of all people! You must do the Battle Square thingy to get his. It costs 64,000 battle points on the first and second disks, and 32,000 (I think) on the third disk. If you haven't done the Battle Square before...I'd suggest waiting until the third disk, getting a ton of GP by racing Chocobos (it takes 10 GP per battle), using Cloud and having him equipped with Ultima Weapon, Slash-All, Enemy Skill (be sure to have White Wind on this, it will come in handy), Zeidrich armor, and a Ribbon accessory. Try getting the status-ailment and materia-breaking handicaps, except Command. These will give you more battle points than normal, and since you have Ribbon equipped, the status ailments won't even do anything to you. There are 8 battles per section, but after each battle, you'll be given the option to quit. Whether or not you complete each set, you'll still get an item called a "Tissue". For all you wondering what it does, this is it: the more tissues you have, the more difficult the battles are. So, I'd suggest trying to get through all 8 battles each time, if you can. Once you've gotten enough, go to one of the computers (there's a dude standing in front of one, and there's another across from him) and on the second page of choices, select Omnislash, and presto! You've got Cloud's ultimate Limit Break! Sorry this got so off-topic, but I like to be thorough sweatdrop

Oh, and it doesn't matter how many levels they go up, limit breaks go up by the amount of times you use them. so its best to train where your characters can get some damage

Oh really? i completely forgot about the cover materia. It's just that while i was training barret and yuffie, the only way their limit breaks went up was for them to receive some serious damage.

yes so does putting the other 2 in the back(there twice as less likely to get attacked in the back)