I think you would find micofiber far too thin and slippery. Go with a heavy upholstery or drapery-weight fabric. Many are water-resistant. Also, consider a pattern that will be forgiving with the inevitable spills that occur at the dining room table. Above all, avoid solid white! If you want something more casual, consider a heavy duck fabric designed for outdoor use--very sturdy & water-resistant.

Or you could have the seats treated with Scotchguard when you have them re-upholstered.

http://crypton.com/

Do you sew or do you need to have these reupholstered? There are tie-on seat covers available in a limited range of fabrics, some shown here at Bed, Bath and Beyond

Here are some instructions for a do-it-yourself chair seat cover. Chair Pad Tutorial

Agree, sunbrella - check them out.

Ultrasuede..Trademarked. It is expensive, but you won’t need that much. I have a bergere chair that I had upholstered in Ultrasuede years ago. Even the cat slept on it. Not a mark on it.

https://www.americanleather.com/furniture-coverings/ultrasuede