Waiting for people -- direct or indirect? Conflicting info in lesson.

Question

I've read the Q&A and related articles and am still confused. The sentence is: My sisters are often late, I always wait for them for two hours. When I apply the information in the lesson's Q&A, I ask myself: "For whom do I wait? For my sisters." Therefore sisters should be an indirect object. However, the quiz gives the direct object pronoun, las, as correct. Which is it and why? (Also, it would be helpful if you edited the questions so the correct answer to this appears consistently.)

ps: it looks like Marcos and Lisa, below, are asking the same question in slightly different ways. Perhaps you can address all 3 questions as a group. Thanks!

Answer

Esperar when meaning 'to remain in a place until someone or something arrives or until [something] happens', is a transitive verb in Spanish therefore the person you are waiting for is the direct object and you should use the pronouns lo/la.

Answer

Hola Pat
As Marsha said, when we use the verb esperar as in waiting for someone, in Spanish, that someone is a direct object (not indirect) -I understand you may be a bit confused with some bits of the explanation in the Q&A; at some point it was mentioned that generally you find an indirect object pronoun after a preposition, but this is very general and it doesn't always apply. 
In Spanish, despite using the preposition "a" after esperar, the verb is considered a transitive verb in Spanish and we need lo, la, los, las. 
It is sometimes useful to check with the diccionary, e.g. wordreference.com and check whether a verb in transitive or intransitive in Spanish. 
I hope this clarified it.
Saludos