I think so too. At least on the literal meaning it really is not harem. However, you need to consider other facts. For example, they are all female. The fiancee, obviously, the two students, the red haired adventrer and the half-sister that's not actually blood related. And now I'm even doubting if the assistant Allen is male or crossdressing.
When the male mc is surrounded by females and all males that appear are either related to the famales (brothers, fathers), antagonistic to the mc or too irrelevant to even be considered side characters... that's when we consider it an harem even if it actually isn't.
Honestly I'm a bit afraid that the 2 students interest and admiration will evolve in the romantic way. It's not weird for female students to have a crush on good looking professors... as long as it stays a harmless crush but it's honestly not something im keen on seein on comics.
But again, there is in fact a subgenre of harem that this fits. The "collector's harem". Where women gather around mc and even if they are not romantically interested on mc they are kept single and having positive feelings towards mc. On thar regard this can in fact be considered an harem.
I do like this story tho and while I find the girls POV annoying, they aren't too irrelevant for the plot so I'm ok with it.
Not a harem, I just read over the spoilers.
I was scared that people were saying that it was harem but as of right now theres not? He has his two students (blonde and white hair), fiancee, and maybe the red haired adventurer. But it would be weird for the CHILDREN to be his love interest but they just seem to have an admiration for him as a teacher. The only real interest should be his fiancee who he states himself he loves because the og villain’s emotions were so strong. I havent read the novel but there’s literally no harem up to Ch.26. Hope it stays that way