Breakdown of Nos gustaría que ustedes les agradecieran a los voluntarios.
ustedes
you (plural)
los
the (masculine plural)
a
to
que
that / than
Questions & Answers about Nos gustaría que ustedes les agradecieran a los voluntarios.
Why is agradecieran in the imperfect subjunctive here instead of the present subjunctive?
Because the main verb, gustaría, is in the conditional tense ("would like"). When a main verb that expresses a wish or emotion is in the conditional or a past tense, it triggers the imperfect (past) subjunctive in the que clause.
Why do we need the les before agradecieran if we already say a los voluntarios?
In Spanish, it is completely standard (and usually required) to include the indirect object pronoun (les) even when you explicitly name who is receiving the action (a los voluntarios). The les acts as a required marker pointing to the volunteers.
Why is there an a before los voluntarios? Is it the personal "a"?
While it looks like the personal "a", this is actually the preposition a used to mark indirect objects. When you thank someone in Spanish, you are literally giving thanks to them. The person receiving the thanks acts as the indirect object.
I've seen subjunctive verbs ending in "-sen". Could we use agradeciesen instead?