we don't need to use at the hotel. we can use in the hotel because it is more informal
Was your answer with "in the hotel" rejected?
I used it, one day later, and it was accepted.
The infinitive of "son", "ser", is used for permanent things, like color (la flor es roja) or personality traits (Ella es amable). The infinitive of "están", "estar", is used for temporary things like location (Las mujeres están en el hotel) or mood (Estoy feliz). Note: these examples DO NOT include all possible uses of ser and estar. I'm just too lazy to type out muchos. ;)