I think Anakin should use a red lightsaber and should get it basically after he turns, I think Palps's lightsaber which he uses to fight Mace should be changed into Vader's one form the original trilogy and have Mace kick it out of Palp's hand to his left onto the floor instead of out the window, then after Sidious says "and we shall have peace" add a bit afterwards where Anakin picks up his lightsaber and just as he's leaving he gets stopped by Sidious who picks up his lightsaber and gives it to Vader (or Anakin) saying "your sith lightsaber" and Anakin replies "thankyou my master" and then the scene ends and goes to the marching on the temple with replaced music instead of the battle theme music.

If that happens then how Obi-wan gets the blue lightsaber is that Vader uses the sith lightsaber through the rest of the film and then at the very end of the duel just after obiwan says "it's over Anakin I have the high ground" when it takes a view from behind obiwan and you see Anakin from a distance just before it goes to him saying "you underestimate my power" have Anakin pull out and ignite the second lightsaber, because at that point he's so angry at Obiwan he'll do anything to show off his true power and kill obiwan, then he jumps at obiwan, gets legs cut, jedi lightsaber lands on the ground (as well as the sith lightsaber) and obiwan picks it up and at this point he's too distracted by the fact his apprentice has been all cut up, is shouting I hate you at him and is then burning to notice the Sith lightsaber, and then you assume that Sidious picks the Sith lightsaber up after the scene where he puts his hand on Anakin's head.