Yes, correct. However, you do not need three applications of the anticommutativity property of the wedge product (on suffices), since scalar multipliers from any factor can be brought out with no other change (linearity of the wedge product).
You are implicitly using the linearity property anyway, by treating (-e1) ^ ... and -(e1 ^ ...) as the same thing before you cancel signs:
-e2 ^ -e1 = -(-e1 ^ -e2) (anti-commutativity)
-(-e1 ^ -e2) = e1 ^ -e2 (linearity)
Manfred