Mine have never gone near their grit so I stopped offering it a long time ago and I have had the same very healthy layers for the past couple of years.
They spend the entire day free ranging and find whatever grit they need all over the yard.
I have never heard of putting grit in the brooder, they get crumbles at that age and don't need it, then they move outside where they find their own grit.
Unless you are feeding them entirely inside their coop and are offering them scraps or whatever I can't see how they would need it.
As for the meatbirds, they are only around for a few weeks and are essentially still babies at the slaughter age, they do fine without grit.
However, I have no idea how long you intend to keep the red broilers for, they grow slower but if you get them out free ranging they will find their own grit anyway.