Will someone have access to your wallet without your device but the person manage to see your private keys and copy them without your knowledge.
Everyone has access to your wallet seed is able to access your coins and move it.
Will the person be able to withdraw your money or change password and block you from having access to your wallet?
A wallet seed contains your private key which is like a key to your house. With that key, everyone can get in your house and steal everything there.
With Bitcoin wallet, we only need private key to move coins.