Hello M. -
I have three sons ages 14, almost 8, and 5 and this has, as you might be able to guess, been an issue we have considerred and dealt with in our nearly-all-male home as well.
What we ended up doing is allowing family-only dinners at home to be "barbarian dinners' complete with elbows on the table, chunks being torn off of the bread, and, honestly, the occasional fart or belch being indulged in and chuckled at.
I know, sounds gross, BUT the trade-off that they agreed to was this: all meals in restaurants and with guests must proceed with the utmost decorum and excellent manners. IF they slip into barbarism in the restaurant or at a friend's house then the next two weeks at home is practice time, so that they can re-learn the proper dinner-out manners.
On two occasions we have had to impose the two-week re-training (no elbows on table, napkin in lap, mouth-closed when chewing, smaller bites, no talking with food in the mouth, asking to be excused when finished, taking own dishes to the sink, and offering to help with clean-up after all are finished), but otherwise our boys are exceptionally well-behaved when eating with others and we are nearly always told by new acquaintances how wonderful our boys are and how exceptional their manners and consideration for others is.
Yes, for me, as a woman, it was not my idea of an ideal meal, but allowing my boys to be boys in all it's glory (farts and all!) has deepened my relationship with all of them and has visibly raised their self-esteem. It has allowed them to stop trying to foist their masculinity on me and to instead express the extremes on occasion only. But with their expressing the extremes of their masculinity they all have also been able to embrace ideals we consider feminine (creativity, art with textiles, knitting, quilting - I am not kidding!). They, and I have become more balanced and happy in genereal and it all started with me agreeing not to banish them from the table for farts, belches, or elbows.
So, my advice, immerse in the barbarian meals at home, complete with goblets or tankards for ales (AKA lemon water, juice or sparkling cider on holidays) on the condition that meals with others be a demonstration of exemplary manners.
Best wishes -