Question

Because the direct object comes before the verb avoir, the past participle must agree with the direct object

Answer 1

Hi,

When the direct object comes before the past participle, the past participle actually agrees with that direct object.

Example:
Voici les cadeaux que les filles ont achetés
Here are the presents that the girls have bought

( achetés is written with an -s to agree with the direct object les cadeaux.)