Causative Verbs and Accusative Pronouns
When using causative verbs like fazer (to make) and deixar (to let) alongside an infinitive, the person being made or allowed to do the action is represented by an object pronoun.
The pronoun you choose depends on the second verb. If the infinitive is intransitive (it does not take a direct object), the person performing the action is treated as a direct object. Use the accusative pronouns: o, a, os, as.
When attaching these pronouns to verbs ending in -z (like faz and fez), drop the -z, add an l- to the pronoun (-lo, -la, -los, -las), and add an accent to the verb: fá-lo (makes him) and fê-lo (made him).
Transitive Verbs and Dative Pronouns
If the infinitive is transitive (it has its own direct object, such as "drink the wine" or "organize the banquet"), a valency shift occurs. Portuguese grammar avoids having two direct objects in the same clause.
The object of the infinitive claims the direct object slot, and the person performing the action gets "bumped" to the indirect object position. Therefore, use the dative pronouns: lhe (him/her) or lhes (them).