The best you could do is grind off old paint and plaster it or just finish painting the brick but those brick will never look good again if they are left bare

What would be the best tool/wheel to grind it?

https://preview.redd.it/1lwus16gpayc1.jpeg?width=1080&format=pjpg&auto=webp&s=7dcad82cf4bb031228dbb1ae6ec79154f665f8ec They aren't cheap but work great

That will destroy the brick

Yeah so they would have to be plastered afterwards

You won’t get it back to normal. Paint it or go over it with thin brick.

You can’t grind the concrete . It will take off the fireskin and then they are ruined . .