Something I always do before feeding is pat my legs and talk about veggies. I make a bit of a song and dance about it. So there's a whole exciting routine that makes it obvious when veggies are coming, every single time. If I am grabbing a drink for myself from the fridge, there's no song and dance of course. My now senior, solo pig, Wiggy perches on when he wants to socialize or have a treat. My other (late) piggy, Bruno, needed lots of floor time to run and forage to burn off energy both mentally and physically - he was a bar chewer. Not sure if more exercise/forage time on the floor might help your piggies with their bar chewing? Maybe not!
I think it is a competitive behavior between piggies too for sure, like, "Feed ME first!" Maybe you could add a chain of cardboard chews along the bars they chew? That's a trick I used that was helpful. I just wrapped cardboard (paper towel rolls) around the bars that were being chewed. That way, if they are chewing, at least it isn't so hard on their teeth. Maybe if you changed your routine to topping up hay 15mins before feeding veggies, and then while they are eating hay, you could bring veggies over? That way, maybe they'd be more preoccupied enjoying a freshly cleaned and topped up hay area and less desperate about veggies? good luck!
