I hope you don't mind me copy/pasting myself!
"It did take a long time for me to attach to her [DD1]. She felt like a stranger for months, sometimes I liked her, and sometimes I disliked her. And i didn't feel i could say anything because you aren't supposed to look at your child and think 'I don't love you, and i dont like you'. It was difficult not to resent her at times which made me feel awful because the adoption was my idea not hers. But slowly I did start feeling love for her. I didn't feel it happen, but when I looked back after 9 months-1 year or so, I knew that if she left my home, i would feel really sad and miss her. And after another 6 months, I would have been devastated had she left. I think it took 18-20 ish months to feel unconditional love
It was really similar with DD2, but it took even longer for me to really love her.
It was easier with DS, maybe because he was quite clingy and wanted me near him all the time (unlike DD1 who was very self sufficient and independent, and DD2 who was very push-pull when it came to wanting me). Certainly, it was easier in that I knew what to expect! When I adopted DD1 I was thown by my own feelings, which made it much harder, but by the time I adopted DS I knew what to expect, so I wasn't beating myself up about my lack of love."
I really did love my DS a lot quicker than the girls (which was because of his dependence and his deep need to be near me and cling to me), but in the end, that doesn't matter, because I'm at the same end point - unconditional love. However long it takes to get there, you get there.
But I am very big on telling people "it often takes time for love to grow, it's NORMAL if you don't feel it straightaway". I've seen so many people over the years who are struggling because of their own expectations of bonding quickly, and so this is one of the things I like to bang on about 
Aside from love, I did feel very responsible for them immediately and determined to protect them all and determined to carry on and keep carrying on. And then it was absolutely 'fake it till you make it'