Translation:You are welcome.
Kembali means to come back while sama-sama means you're welcome/you are welcome. Sama on its own means same, but if you say saya terima kasih kembali that means I am returning the thanks. You could instead of Sama-Sama say Masama, which means the same thing but is very informal Indonesian, just like "Makasih" which is Thank you.
I disagree. There is a difference between "you are welcome" and "welcome" if you say them without context. The first is a response to "thank you" while the latter is a greeting.