Meeting boyfriends brother for the first time?

I've been with my boyfriend for over 2 months now and I've met his mum and her partner and apparently I left a good impression for them and they are both lovely people. I'm meeting his brother and sister-in-law tomorrow as well and we're going out for lunch together and I'm pretty nervous about it. I've never been formally/properly introduced to an ex's sibling before~ probably partially due to them not being close. My boyfriend and his brother have a very close relationship and both him and the sister-on-law are eager to meet me. I'm very flattered that he wants to show me off to his family :)

Any advice on how to act? What to say? I can get shy at first around new people (though I try and not show it) and it takes me a while to open up to new people. Another thing is, they have 2 young children who presumably will be there, and I get quite awkward around children (not intentional but never grew up with young relatives or anything~ how should I act around them?

Also any advice on what to wear? It's not a fancy place we're going for food, just a relaxed pub lunch. I have a gothic boyfriend and his brother and sister-in-law have both had alternative phases and likewise, I have an alternative look to me.
Meeting boyfriends brother for the first time?
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