I'm now writing on behalf of the classmates to invite you to come and attend our farewell party on Saturday.

我代表全班同学给您写信，邀请您来参加我们的送别晚会。

Shall we have a farewell party?

我们要不要来个告别晚会？

We should hold a farewell party for you.

我们要为你们举行一个告别聚会。

We're planning a farewell party for you.

我们准备给你开一个欢送会。

We'll hold a farewell party for you tonight.

今晚我们会为您开一个欢送会。