Israel has most definitely replaced Christ in these last days. So yes, replacement theology would seem to be alive and well.
Yes, the term "My brethren" are unquestionably Jews of the Nation Israel, as the saved gentiles are seen in verse 34.
I suppose your pastor has failed to teach you these passages? Well it's your lucky day now you know.
So then, time for you to......choose sides.
I urge you to.....choose wisely.
[Mat 25:31-34, 40-41, 45-46 KJV]
31 When the Son of man
shall come in his glory, and all the holy angels with him,
then shall he sit upon the throne of his glory:
32 And before him shall be gathered all (GENTILE) nations: and he shall separate them one from another, as a shepherd divideth [his] sheep from the goats:
33 And he shall set the sheep on his right hand, but the goats on the left.
34 Then shall the King say unto them on his right hand (SAVED GENTILES) , Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world: ...
40 And the King shall answer and say unto them, Verily I say unto you, Inasmuch as ye have done [it] unto one of the least of these my brethren, ye have done [it] unto me.
41 Then shall he say also unto them on the left hand (UNSAVED GENTILES) , Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels: ...
45 Then shall he answer them, saying, Verily I say unto you, Inasmuch as ye did [it] not to one of the least of these, ye did [it] not to me.
46 And these shall go away into everlasting punishment: but the righteous into life eternal.