‘Were’ needs to be replaced with ‘was’ to make the sentence grammatically correct. This is because, ‘If the subjects are joined by as well as, with, along with, together with, and not, in addition to, but, besides, except, rather than, accompanied by, like, unlike, no less than, nothing but, led by, headed by, guided by, controlled by,governed by,etc.. Then the verb will agree with the first subject. Thus, the correct formation would be, ‘The teacher as well as his wife was invited’.
