Well, you might find it more beneficial to look at the whole story, in particular the epiphany of Gabriel Conroy at the end of this brilliant tale, and the way that he realises central truths about himself and how he has been living his life as if he were dead.
However, to restrict my answer to the setting of the party as directed in your question, it is important to note the number of dead people that are mentioned in this large section of the story. Consider how Gabriel remembers them in his after-dinner speech, and various characters who have passed away are mentioned during the course of the story, including Gabriel's mother, his uncle and his grandfather. Consider what Gabriel says in his speech:
But yet, continued Gabriel, his voice falling into a softer inflection, there are always in gatherings such as this sadder thoughts that will recur to our minds: thoughts of the past, of youth, of changes, of absent faces that we miss here tonight. Our path through life is strewn with many such sad memories: and were we to brood upon them always we could not find the heart to go on breavely with our work among ht eliving. We have all of us living duties and living affections which claim, and rightly claim, our stenuous endeavours.
Such words recognises the coexistence of the dead among us: not in any spooky ghost-like way, but in the way that our memories and longing for them intersect with our everyday lives.
However, if we consider briefly the most important dead person that is mentioned, Michael Furey, we can see how this division between the dead and the living is somewhat complicated by Gabriel's realisation that there are so many people who live their lives as if they were dead without actually ever living. At the end, the snow falls covering both categories of people.