Is a brown parakeet cere normal? How do I tame my scared parakeet?

Both your birds look pretty young still! Cere color changes are normal as parakeets reach sexual maturity. Females will typically get a pinkish or brownish cere when they are ready to breed, while makes will often get a deep bluish cere. Younger birds can have a mix of colors that will deepen/change as they become mature.

As for taming, if you find they have a favorite treat, such as a piece of fruit or spray of millet seed, etc, you can use this to help them get used to you. Every time you approach their cage, you can offer a bit of treat until they are comfortable having you around. From there, you can move onto offering the treat to be taken from your hand, and then work up to petting or even handling them, each time offering a treat. If they become too nervous or upset, simply go back to the previous step they were comfortable with and try again from there.