"Selamat datang, silakan."
the "come in" part is actually just implied by the circumstance. It directly translates to "Safe arrival, please." Just as Selamat Pagi is literally "Safe Morning" as in 'I wish you a safe ...' But as English speakers do not use this form of greeting, we understand it as 'Welcome,' 'Good Morning,' etc.
"Selamat datang" means welcome, or something like, "I am pleased that you are here". For example, "Welcome to our town". "Sama-sama" is the equivalent of what American English speakers mean when they say, "You're welcome!" after somebody has thanked them. In other words, "No need to thank me".