How Long After First Kitten Is Born?

How long after first kitten is born?

I have a one-year old Siamese. He recently got another Siamese, but they are treated as brothers. The new guy has been with me for two weeks now and he’s the only sibling I’ve ever had! They both eat well (one cat eats quite a bit of food & the other not much), play well together all day long, sleep super peacefully at night w/o fighting or anything like that — it’s just that neither will allow me to pet them or pick up either of them because they don’t want to be picked up by anyone else, even their own parents! My vet says this isn’t normal behavior for cats. Is there something wrong?