Consider this verse:
John 18:28, KJV "Then led they Jesus from Caiaphas unto the hall of judgment: and it was early; and they themselves went not into the judgment hall, lest they should be defiled; but that they might eat the passover."
We know Jesus had already eaten the paschal meal the previous evening, and we must assume all the other Jews had done so also. To me, this verse indicates the Jews considered the Days of Unleavened Bread as part of the Passover observance, and the unleavened bread made especially for this observance as an item of this observance which they couldn't eat if they were ceremonially defiled. This bread is what John was here referring to as the "passover".
Dr. Thomas Cassidy has suggested that there were TWO paschal meal observances, one date being observed by the Southern Jews, & another being observed by the Northern Jews. I reject such a notion, as I've never seen one shred of evidence to support it, and I KNOW that sinless Jesus observed it at the proper time. Had He NOT observed it on the correct date, this alone would have been grounds for the Jewish leadership to have killed Him. WE KNOW they had no LEGITIMATE charges against Him, that they invented their accusations. Had He not observed the paschal meal at the correct time, they would have brought that against Him. Therefore we must assume that the Jews who arrested Him had also observed Passover at the correct time and that John 18:28 is referring to the unleavened bread made specially for the Unleavened Bread observances during Passover week.
As for the HIGH SABBATH mentioned during the crucifixion account-this was almost certainly the HOLY CONVOCATION called for in Exd.12:16. The ONLY work permitted that day was the serving and eating of their food. Therefore, the Jews COOKED it or otherwise prepared it on the previous day. Seeing as how the Jews reckoned the beginning of a new day at sunset of the previous one, its easy to see that they prepared their food in the afternoon before sunset, and ate some of it that evening after sunset while having prepared enough to last till the next sunset.
The first editions of the Geneva Bible rendered 'pascha' as 'Easter' in several verses. However, the 1599 edition had corrected all these, rendering 'pascha' as 'passover' every time. The AV translators simply dropped the ball by saying 'Easter' in Acts 12:4, especially since they included Easter in the AV 1611's List of Holy Days, but not Passover, and there was absolutely no justification by context for them to have said 'Easter'.