If I use instacart for shopping at Costco do I have to be a member of the store ??

Get a prescription sent there. ... they won't turn you away

They check your membership card when you enter and require it again at checkout no matter what form of payment you use. Basic membership is $60 per year and most people find they save far more than that.

Members only and they get right on you at the door

ditto

Yes

Technically you wouldn't need it, but the person who physically gets your order would have to be.

They won't let you in you're not a Costco member.

They like you to be member for everything