I beat it how I don't know but I did. The last ones are pretty hard since you are by yourself. I would level up all the way and use any power, defense, and magic boosts you have left.
As for tips, well just try to keep your health up. And if you are trying at the very end with all the FF characters try to take out Yuffie first since she can heal everyone. And then I say take out Tifa then Leon and then Cloud.
But I know when I did it I got really lucky, since I was using the Ultimate Keyblade my MP would rush back really quick and I could keep healing myself.
I don't think I helped much just keep trying you should get though it some how.