Wow how exciting for you to be meeting your birth family! Hope it all goes well for you, good luck.

On the gifts front I have an 11yr old an an almost 10yr old myself so I have a bit of experience in this field. Of course it all depends on how much you want to spend and im thinking its not too much so lego is always a winner. They have heaps of little box sets they can make up. Anything Star wars is a winner in my house, as is Transformers. Bionicles is another sure fire hit. My older son is very much into music at the moment so a cheap mp3 player would be an idea if you didnt want to go the toy way. But I have to say that thats all they are really interested in at this stage.
Anyway hope this helps a bit an again good luck x