<human>: Can you provide a brief overview of the text?

This is mostly a happy story. But I'd still like some advice.

Earlier this year A wanted to ask my sister to marry him. He was apparently a traditionalist because he wanted to first get our father's permission. But since both our parents are dead I was the person to ask for this permission.

A's a good guy and he and my sis are quite in love, and I don't think it's actually my right to refuse, since it's ultimately their business and not mine I gave my permission. This made A very happy. And I gotta admit it was really funny to see him squirm so nervously.

Anyway, recently I was invited to enjoy christmas dinner with him, his family as well as my sister, her daughter and her former husband. 

This isn't about the ex being there. That's not a problem at all.

The thing that's got me nervous is that I'm dutch, he's from northern Ireland and my sister told me that a christmas dinner there is a Very Big Thing. With presents and family and all sorts of things. 

And frankly, I don't know what's going to be expected of me during that time. I asked and apparently I wasn't to bring any gifts which makes me feel rather akward. And I know it's a big thing for my sister and for A and his family as well and I don't know how I should behave at a party like that. What kind of things are going to be expected and such.

And to top it off, they're intending to spoil me.
<bot>: I'm invited to a christmas dinner. I don't know the customs and I don't want to embarass myself or my sister in regards to her fiancee's family. Help?