Learn Spanish (Latin America): A ellos les interesa la música.

With verbs like interesar and gustar, the sentence works differently than in English. The thing causing the interest is the actual subject of the sentence. Since la música is singular, the verb must be the singular interesa. Literally, this says 'The music is interesting to them'.

Why do we use both a ellos and les?

They both mean 'to them', but serve different roles. The pronoun les is required to show who is receiving the feeling. However, les can mean 'to them' or 'to you all'. Adding a ellos at the start clarifies exactly who you mean. It also adds a bit of emphasis, like saying 'As for them, music interests them'.

Why is there a la before música?

In Spanish, when you talk about a noun in a general or broad sense, like music in general, you must include the definite article (el, la, los, or las). Because music is the subject of this sentence, the la is absolutely required here.

Can I change the order and say La música les interesa?