The passover was "eaten", not, 'between the Evenings' [behn-ha-arba-yim], but, "late" [ereb], "in That Night solemnly to observe". The passover lamb was sacrificed, 'between the Evenings' [behn-ha-arba-yim], not "late" [ereb], "in That Night solemnly to observe".
And 'after it'-- 'it'--"the first, first day they killed the passover" = "removed leaven (life) on" (Mark 14:12 Exodus 12:15), followed the first day they "ATE unleavened bread with, the flesh" -- in Exodus, "on the fourteenth"; in subsequent Scriptures, "on the fifteenth day of the First Month". Then for six more days, they ate only ulb with no flesh.
Q~So why would those with our Savior think that there was a need for something for the Feast if it was already started~Q, ? Quite right! Non the less, 'during the High Sabbath', they did buy-- things that ought to be provided on or for 'the High Sabbath'. Yes, 'everyone is at the Feast within their homes, the Whole City is shut Down, and giving to the poor for their Feast' took place... outside their homes! And if something was needed for "that great day of sabbath of" the passover, it had to be made available, and if needed for the sacrifice to be eaten "at That First Night" John 19:39, it had to be made available even to the rich, especially if needed for the sacrifice to be "treated ... according to the ethical code of the Jews to BURY"! It would not be too late.
And if you read, you will find that the priests that morning still, would not enter the hall of judgement so as to not defile themselves, that they could EAT the passover "at The First Night" after this day of sacrifices! Hundred percent! But of course it did not work out according to their plans, but according to God's plans.