Matthew, Mark, and Luke each seem to put Passover on the first day of the Feast of Unleavened Bread, but a closer look reveals the consistency of Scripture.
The context of Deuteronomy 16:1-3 indicates the focus of these verses is on the Night to be Observed and the Days of Unleavened Bread rather than the Passover.
Jesus and His disciples are shown observing the Passover in a home at the beginning of Abib/Nisan 14. However, a few verses seem to indicate the next day.
At the time of Christ, because of historical deviation, some kept Passover at home at the start of the 14th and others kept it at the Temple at the end of the 14th.
Some believe in a late-14th Passover on the basis of II Chronicles 35:10-11, but this overlooks the context. The Passover was originally a home-based observance.
The temple Passover commanded by Hezekiah was a very unusual circumstance in which the king centralized worship to keep Baalism from defiling the Passover.
Nine steps had to be included with the Passover observance, all within the house until morning. It takes place between sun's setting and complete darkness.
Major reinterpretations have significantly distorted the meaning of Passover and Unleavened Bread, blurring the distinction between the two events.
The Passover is to be kept on the twilight of the 14th, while the Feast of Unleavened Bread begins on the 15th. The Word of God supersedes tradition and heritage.