I was also having problems with 251, which is how I found this post. I eventually figured it out on my own...
BARAKA: This is incredibly easy if you just time uppercuts. When the match starts, immediately crouch and wait to uppercut him; he'll jump or walk towards you over and over. After you uppercut him, immediately shoot a flaming skull (back, back, X) and you'll hit him more often than not. Keep repeating this cycle of uppercuts and flaming skulls until he's dead. The only time he'll hit you if your timing is correct is when he charges with both blades thrust out in front of him (and you can hit block to prevent that if you've got serious reaction time skills). Conserve all of your super meter for Sindel. Baraka should be incredibly easy. By the way, this strategy works in all modes, in all difficulties, for beating Baraka.
SINDEL: Get at a distance, and use enhanced flaming skulls (back, back, X + RT) over and over until you run out of super meter. Once you're out, start using regular flaming skulls over and over (back, back, X) to kill Sindel while recharging your super meter for Shao Kahn. She'll shoot purple energy at you, but your fireballs will kill her way before she'll kill you, and the damage you take will be minimal after the heal between enemies. This is also pretty easy, once you get the timing down.
SHAO KAHN: Alright, so you've heard the rumor...get at a distance and shoot flaming skulls over and over. But use enhanced flaming skulls to even this match out. When he gets in close, don't crouch; just stand normally, press block when he charges or swings the hammer, and react with uppercuts or sweeps. Once you hit him with an uppercut, jump back into the flaming skull pattern. You cannot block his flying hammer, so when you see it come at you, jump. Using X-Ray is pointless here; use your super meter exclusively for enhanced flaming skulls. This one is the hardest, and if he hits you with his X-Ray, it's usually all over, so be prepared to jump up and back when he goes into the opening move.
Hope this helps somebody! The Baraka strategy is probably the most valuable, as it applies across the entirety of the game.