I found out in my late twenties that BOTH my parents had, with other people, had children that were subsequently adopted..
My mothers child I have never met, nor did she, I have no idea if she tried to track him down or anything, he was adopted at a few weeks old from a mother and babys home somewhere in devon (in 1967 i think)..
My fathers son however, my halfbrother, is now a part of my life.. he's a good bloke.
However you feel.. is normal, for you. I distinctly recall adding up my mother having a son she had to give away, with her dissatisfaction with me and my sister as children, we were NOT the son she gave away, we were not the 'do-over' she hoped for and nothing we did was ever really good enough.
My dad, on finding his son and getting in touch, did initially do the 'woohoo ive got a son isnt it fabulous wonderous brilliant' etc...
And this wore off after a bit, as it turns out, his son has FAR more in common with me and my sister than with him - all things my Dad has little interest in or doesnt 'get' (music, animals, art)..
Just see how things pan out - you can feel angry and grumpy and confused and pushed out and all of those things... just strive not to be a cunt to anyone because of those feelings, and see how things go.