Learn Spanish (Latin America): Nos encantaría que ustedes usaran la parrilla. - We would love for you guys to use the grill.

The main verb encantaría is in the conditional tense ("would love"). When you express a wish, preference, or emotion in the conditional, and there is a change of subject in the sentence—from "us" (nos) to "you guys" (ustedes)—the verb in the que clause must take the imperfect subjunctive form.

Why is it Nos encantaría instead of Nosotros encantaríamos?

The verb encantar works just like gustar. Instead of saying "We would love it," the Spanish structure is closer to "It would enchant us." The "it" doing the enchanting is the whole idea of you using the grill (que ustedes usaran la parrilla). Because that entire idea counts as a single singular subject, the verb takes the singular form (encantaría), and the indirect object pronoun Nos shows who receives the feeling.

Could I just say Nos encantaría que usaran la parrilla without ustedes?

Yes, you can drop ustedes if it is already obvious who you are talking to. However, because the imperfect subjunctive form usaran can mean "they used" (ellos/ellas) or "you all used" (ustedes), including ustedes in the sentence is a common way to avoid any ambiguity.

I've seen imperfect subjunctive verbs ending in -se. Could I use usasen instead of usaran?