"We all teachers" is certainly not grammatical English. "All us teachers" is acceptable, though analysing why is tricky.
You can form a noun phrase from a pronoun+noun placed in apposition:
We teachers are strong.
He gave us teachers a pay rise
Us teachers want more! (*)
The meaning in each case is "us, who are teachers". A normal apposition
The last example is doubtful, because "Us" appears in the subject, but examples similar to this in considered speech of native speakers do exist.
The word "all" functions as a determiner, and it should not be placed in the middle of the apposition. So "We all teachers" is not correct, but "All we teachers" might be ok.
All can also be a (pro)noun, and you can form a noun phrase "All of us teachers". The subject is "All", "of us teachers" has "us teachers" not in the subject position, and so "us" is used in preference to "we".
"All us teachers" can be parsed either as a reduction of "All of us teachers" or as a modification of "All we teachers" (with us used as the pronoun is not a major part of the subject).
If I was speaking I'd prefer "All of us teachers..."