Hey Solomon:) If you're inviting your friends to a house party and you want them to enjoy the food without reservations, "please help yourselves", is a great phrase to use in this scenario and very commonly used. Also, you could say "tuck in everyone" or "please enjoy the food". "Stand on ceremony" is quite uncommon to use. To "stand on ceremony" is to behave in a formal way. It would make sense to use it by saying, "please sit down and make yourselves comfortable, we don't stand on ceremony here." I would suggest a more common idiom to use in this scenario after telling your friends to enjoy your food would be "make yourselves at home". This is a lot more colloquial. For example, "please don't be shy, tuck into the food" followed by "make yourselves at home everyone, enjoy".

No, I don't think it's used colloquially, except perhaps in a joke, maybe. You can say "Make yourselves at home" or "Eat as much as you like/want", for example. No worries! :)

I just remembered that you were asking about the phrasing in terms of offering food. A good phrase to use can be "help yourselves to the food." You could even say something like "eat as much as you'd like." Hope that helps!

Hi Solomon! As an American native English speaker, I have never heard the phrase "stand on ceremony." Perhaps it's more of a British thing? Either way, the comment above covers it well. In the US, it's common to say something like, "make yourselves at home" or "don't be shy, make yourselves at home." Something like that.