I am atheistic and agnostic personally, so not speaking from faith but:

People can have two (or more) emotions at the same time, they can be happy and joyfull that their relative is in a better place now and at the same time sad and tearfull that the person is no longer with them. Happy for the dead, sad for themself.

It is not a contradiction, it only shows the very deep and complicated ways of our mind and emotions.