They were commanded by God through Torah to eat the Passover. To say that this is anything other than the Passover feast would be in complete error and a total disregard for the Scriptures. The only accuracy in this is that it was the last supper that Messiah ate. Easter is celebrated by the Church as the commemoration of the resurrection of Messiah. It is celebrated in the spring according to the vernal equinox.
Easter is strictly a tradition of man.
There is nothing to validate the institution of the celebration of the resurrection by the disciples or the early Church. In fact, His patience is tested with traditions. Israel only honored God with their actions, not with their hearts. The people had begun to walk in their own way and in the desires of their own heart. They did not listen to God, instead their evil increased.