"True/false" refers to reality. If something is "true", then there is proof of it in reality. You meant to use "correct/incorrect". If something is correct, it is technically perfect and without errors.
1. "They won't appreciate us." If you use "appreciated", then you need "to be" in front of it: "They won't be appreciated (by us)." However, the action is completely reversed.
2 "I am afraid of dogs." This is a collocation you just have to learn: afraid of ___. No other preposition fits.