Interesting subject to look at for certain. Your thesis rests on the assumption that Scriptural references to "the Passover", during the time between Jesus' arrest and execution, should be understood, not in reference to time when the Passover (sacrificed lamb) was prepared/eaten, but rather the entire "Festival of Unleavened Bread" which was a week long festival. Is there a basis for this?
As I understand "the Passover" refers to the sacrificial lamb that was prepared and eaten during Nisan 14/15. So why, according to your timeline, is Scripture still speaking of the Passover on Nisan 18, 19, etc.?
Added: Specifically look at John 18:28, where is says they wanted to keep clean so that they could "eat the Passover". Since "the Passover" is specifically the sacrificed lamb - what do you propose they were concerned about eating?
One More Addition: Take a look at Exodus 12:21 where the Jews were intructed to "slaughter the Passover". They were not killing a holiday or a festival but a lamb. I know in modern times Passover refers to a Holiday but in the Bible it is in reference to the sacrificial lamb. Compare to how Paul refers to Jesus as "our Passover" at 1 Cor 5:7.