Well, do not expect these plywood stairs to wear like true solid wood ones. The plywood veneer used today is paper thin. You can not even sand it except with a very fine abrasive. The core material is mostly softwoods, so again, you not not the the dent resistance of hardwood, but whatever the softwood core material is. IMO, you are using the wrong material. Plywood was not made for this purpose.
Instead, considering finding a local source for 5/4" hardwood planks. Three 4" wide planks will make a 12" wide plank, enough for a tread. I've built my own treads before and it's easy. I use a biscuit joiner and clamps to glue up the strips into treads. Find 5/4 stock SAS 4. Arrange the pieces in the most pleasing grain and color pattern. slot them, add biscuits, glue and clamp em.
After gluing, sand and round over the front edge for the nose. Now your ready to finish them before installation. Much easier to do the finishing now than after they're installed.
Another tip. You can use a wide variety of wood. It doesn't have to be oak or maple ( although those are nice ). If you find a source for another wood that saves you lots of money consider that. Some wood alternatives: Birch, Alder, Beech, Doug Fir, Southern Yellow Pine, Poplar, Mesquite, etc. But please note, many of these are softer than oak and maple and will dent easier. But they are real wood and can be refinished many times.
And actually, around here, oak treads can be had for under $30.00. That's $400.00 in treads and no dicking around with trying to build something that will need to be ripped out later, just to save $200.00?