Tifa's battle style is very direct, she always rushes Sora, making it difficult to block her attacks. Yuffie will constantly teleport around hurling shuriken at Sora, but Donald and Goofy are present making the battle easier. Be certain to use Final Form during this battle.
Yuffie will be an annoyance as she will constantly interrupt Sora's attacks on Tifa. Try to get behind Tifa and avoid staying in front of her. She can use her Final Heaven attack, which deals major damage, as a combo finisher whenever she chooses. Try to focus on Tifa as she is the stronger and more dangerous of the two, but watch out for Yuffie.
When Tifa comes up close and starts her punching combo, use Reflega immediately or Sora will suffer major damage. Tifa is weak against Reflega so be sure to use it as much as possible. If interrupted while doing this Glide or run away, because if Tifa shouts "Here we go!" or "Don't say I didn't warn you!", she will jump high in the air and yell "Final Heaven!" which will launch several explosions in front of her. This attack can cause major damage and cannot be stopped.
The second time around, Tifa is with Cloud.
Equip all of the following abilities:
Equip the Ultima Weapon Keyblade for MP Hastega. Also equip any accessories that will increase Sora's Defense and Magic stats. For the shortcuts, it's recommended to have Curaga, Thundaga, Blizzaga, and Reflega.
This battle is against Tifa along with Leon, Cloud, Yuffie. This battle can be very difficult. Tifa can cause massive damage with close and mid-ranged attacks. Cloud can't hit Sora from long range, but he's fast enough that it hardly matters. Leon can shoot fireballs, but they can be dodge fairly easily. Yuffie can teleport and enhance her shuriken with magic, and also can use it in a huge area attack.
Jumping and Aerial Dodging as high as Sora can before gliding away are necessary for survival. For offense, Thundaga should be used whenever possible.
It's recommended to defeat Cloud and Yuffie first they are able to cross the battlefield faster than anyone else. Don't worry about attacking anyone else, but keep an eye out for their attacks—Cloud and Tifa in particular are very dangerous, and so is Leon when he activates Blasting Zone.
Whenever needed, heal with Curaga and run away until the MP Charge has finished, at which point continue using Thundaga.
After defeating Yuffie, begin attacking Cloud. Cloud's strongest attack is Omnislash—he'll start crackling with blue electricity, and then start moving much faster than normal. When he starts this move, just repeatedly use Aerial Dodge and Glide to run away until he slams his sword back into the ground, signaling the moves end. From there, continue attacking him with Thundaga.
When Cloud is defeated, focus on Tifa. Mostly, she'll just use martial arts-style attacks, but some of them like Water Kick have range to them. If the pair starts swarming Sora, go ahead and use Reflega for defense. Start using Keyblade combos now, since Sora is more likely to survive more than just a couple of hits.
When Tifa falls, heal and use Berserk Charge on Leon, hitting him as much as possible until Sora finishes recharging MP and he can deal the finisher. Then use Trinity Limit to land a few more hits on them and bring Sora back to Berserk Charge. Repeat this until the battle ends.