I was just about to make a similar post when I spotted Wendy's post
I also have 2 littermates - Bella and Cinders. They're 5 months old and I've had them for 8 weeks now.
Bella is very affectionate and friendly and is always happy to let me pick her up for a kiss or cuddle or strokes but is happiest lying on her back having her tummy and armpits tickled. She also purrs at the drop of a hat. Having said that, she won't settle down in my lap.
Cinders is affectionate but it's on her terms. If I try to approach her to give her affection, she will run away. When she wants to be stroked, she lets me know by rubbing herself against my ankles and/or meowing until I stroke her - her purrs would put any sports car exhaust to shame!
She doesn't like being picked up and will struggle to break free if I do manage to pick her up. However, she does occasionally climb into my lap and will stay there as long as I don't attempt to stroke her. (I am only allowed to stroke her when she looks at me and meows her permission!) If she is very tired, she will roll onto her back in my lap and let me tickle her tummy and armpits
I think Cinders likes being around me but maybe isn't so fussed on lots of direct attention. I try to spend at least half an hour every evening playing with the kittens and Cinders is always happy to play. Whatever room I am in, both Bella and Cinders will follow shortly - it's rare that they are not in the same room as my husband and I. At bedtime, Bella will curl up under one of the bedside cabinets and Cinders will either sleep on my legs or between my husband and my heads in the gap left by the pillows
Having read what everybody else has said and looking back on what I have just written here, maybe I don't have a shy kitten. Perhaps it is a case of they are just 2 different personalities