Help! Kitten with split personality?

I have 2 kittens from the same father (different mothers). One is 2 weeks older (16 weeks) and she has a great and outgoing personality. The younger one shows lots of affection when she is separated from her sister. For example when I take her into another room by herself she turns into a different kitten, totally won't leave me alone and is so affectionate. They love to play together and get on fine, neither dominate for what I can see. What can I do to help the younger one come out of her shell more?

Thanks heaps
Phebe

IMO, your younger kitten sounds okay. She's being affectionate in her own way.
Perhaps in time and watching her older sister she may decide to join in the fun.

Don't push her to do anything she is not comfortable with. Unless these cats were bred in controlled environments, it is possible that there is more than one father-if the cats are backyard bred. More than one tomcat will mate with a female in heat-