I know isekai manga has trash tier writing, but this right here is a new low
the word used is 捨て身の人間 (sutemi no ningen) sutemi=sacrifice/discard,
no = (the word come before NO describe the word after it)(ab-nominal modifier). ,
ningen=human/person.
So rather than "self sacrificing human" it is more of a "sacrificial human". Cannon fodders, fanatical cannon fodders. In context she is referring to the cult members that will fight to the death.