Sometimes suckling on things can be a sign that the kittens were taken from their Mum too early, if they came from a petshop, there is no way of knowing what their early socialisation experiences were. Do you know how long they had been at the petshop? That would have been a very very stressful time for the kittens, and although you are giving them the time you can, the reality is they are both very young, and mostly alone all day. Hopefully he will become more settled and secure as he grows.

__________________