I've always thought of this as "make yourself at home" or "make yourself comfortable". Would it mean the same thing?
Yeah, "make yourself at home" would be a better translation. This is an English saying though. A Vietnamese saying would be "tự nhiên nhé." We wouldn't say "làm ơn."
Lol. We only use làm ơn as in Làm ơn cứ tự nhiên! if we're annoyed by someone doing something stupid but we try to be nice to them instead of shouting Just !@#$ do whatever you @#%^ want to do!
I totally agree with you. My mom uses it when she is nagging me.
So what would the plural be? (for "help yourselves")
Help yourself = Help yourselves: Cứ tự nhiên [informal]; or
Help yourself = BẠN cứ tự nhiên; Help yourselves = CÁC BẠN cứ tự nhiên [formal]