Yeshua celebrated the annual appointed feasts, the apostles did likewise, ALL being Jews. There is no evidence that early Jewish believers did not either. A Jew does not "become" a Christian. Yeshua was the promised JEWISH Messiah. Implying belief in their own promised Messiah somehow converted them to a new religion is ridiculous.
Regarding the term "Easter"...it is in no way any kind of translation of either the term Passover, Pesach, Pesakh or Pascha. That may be the way it is being used but it is not originally the definition of that word. The origin was the pagan goddess of spring Oestre.
It IS Pascha not Easter!
The day that Chametz is put away is historically the 14th, the preparation day. The seder is held on the night of the 14th which is actually the beginning of the 15th, Passover. Both Pascha and Pentecost are JEWISH words. Pentecost or Shavuot, was held 50 days after the counting of the omer began.
Historically, it was on the 14th the lambs were killed. Yeshua likely held His seder the night before if He was to die on the day the lambs were killed. Either way, John, Polycarp and the east held Passover as a memorial of the death of Yeshua as He commanded them. It says, In the first month, on the 14th day of the month at twilight is the Lords Passover. Then on the 15th day of the same month there is the Feast of Unleavened Bread.