Los Vs Les
 

In the two sentences below, them represents a direct object, so we need to use los. Is it possible to replace los with les? If so, would it make a difference if 'my friends' were all male, or if they were a group of mixed gender?

My friends want me to bring them to the cinema:
• Mis amigos quieren que yo los lleve al cine.
• Mis amigos quieren que yo les lleve al cine.

Many thanks in advance.

Using "les" would be an instance of "leísmo", an anomalous construction, in this case, a somewhat accepted use -not in my country and a few others, where it sounds something between horrible and excessively polite-. Using "los" is the only correct way -for me, it is; for others, they'll have to reluctantly say it is though they may keep using "les"-.

About "los", you should use it whether they are 10 male friends or 1 man and 9 women as "los" is in fact the default for genderless, something most native speakers don't get.

"Mis amigos" is an indirect object, so the grammatically correct pronoun is "los", but in some regions the generalized usage is "les", so it's acceptable, depending on where you are.

Mis amigos quieren que yo los / les lleve al cine.

1. I would say Mis amigos quieren que les lleve al cine (without "yo"). If you say "yo" you give big importance to be you the person to bring them to the cinema.

2. About los or les I will try to explain you wuth a different example:
- Les curo las heridas
- Los curo las heridas
I think Les curo las heridas is right and Los curo las heridas is wrong.

Your (2) is not related with this thread's question. With "los" it would become a "loísmo", a different kind of creature.

If you are familiar with the function of the direct and indirect object pronouns in English, it will help you figure out when to use los (direct object) and les(indirect object pronoun).
The rules are mostly the same. PS: I get it wrong sometimes, but so do native speakers.

Do you mean direct object pronoun? (if I'm mistaken, then my apologies)

:duh: Of course. I'm sorry.

Indirect object -> "les"
Direct object -> "los"

Thank you for noticing the mistake. :)