:)
Here, my friend, "εις", insofar as you were quoting +Luke, would have been just fine, as in "...εἰς τὴν ἐμὴν ἀνάμνησιν". It means "in". "Εστι", or "εστιν", means "is". But you are doing good. Keep it up. If, by the grace of God, you gain a working knowledge of Greek, it will open a whole world of scriptural understanding for you, which, aside from the spiritual benefits, will allow you to astonish your friends and confound your enemies!
Would that we were all Hebrew and Greek scholars, we could argue on a more elevated level, but I truly do not have the time available to do a study justice and no interest in being another dilettante scribbler.
So in lieu of that I’ll rely on the Gray Beards of Greek (like yourself) to correct my errors.