Supposedly, "you are welcome, you're welcome" is 不客气，no worries is maybe 没关系,maybe 别担心吧. I think "you're welcome" like 欢迎, it's said after someone says Thank you but... I haven't heard it in a long time. It's also used in other contexts "Welcome to our humble home." "You're welcome to anything in the refrigerator if you get hungry." People say "no problem" a lot... or "sure" in response to "Thank you". "Thanks". The other four, besides "you're welcome" are often said when either someone makes a minor mistake and apologizes and one wants to accept their minor apology for something. Etc. Actually, I always worry about saying 不客气 rather than something more like 别客气, I worry that I'm saying that they're rude or something unintentionally. Also, if you offer to do something and someone says "that's alright", it means they don't want you to do that thing or they don't need you to do that thing. If you're apologizing for something and they say "that's alright", then they're accepting your apology and telling you not to worry about it. But if, for instance, you're making plans to do something, and you say "How about tuesday?" And they say "tuesday would be alright", then they're saying that tuesday is a good day. But "that's alright", that pronoun, typically means they don't need you to do that thing. You can always ask the person what they mean if you're unclear.

多用在人家说thank you 之后。