What should my sister say when she brings her boyfriend home for the holidays?

Depends on what you say. When you respect each other, you should address them first. I don't know if you can take the opportunity to ask, and then if you are an elder or a leader, simply say some blessings, not too many words. If you are a stranger, simply express your first acquaintance and give some advice. When these are the most simple and omnipotent toasts, if you want to get down to business, you have to find out the meaning of this drink and the general idea of everyone.