There is a really wide range of paver options, and they can vary locally because most pavers are manufacturered within a few hour drive of where they are sold (weight and freight makes it not common to ship across country). Belgard has manufacturing plants around the country, but not necesarily the same types/shapes/colors of pavers sold on the west coast as the east coast. On our area, Belgard has 6-7 different types of pavers that range in price by over $5 per square foot, so just having a quote that says "belgard pavers" still doesn't actually say what you are getting. It's kind of like getting a quote for a "Ford" car- you need to specify what type. Ask where your contractors buy from and go look at the different types (and other brands). Pick one you like and the ask all companies to quote that paver so younare comparing apples to apples. Belgard makes good products but in our area I wouldn't say they are the only good paver brand, ask experienced contractors in your area and they can recommend what pavers they feel are good (and which to stay away from). I like paver driveways - no cracking (which concrete does in our climate), beautiful, last longer than asphalt, and weeds can be managed by good installation, proper drainage, and maintenance.

I think this paver would be a good option for the three different colors you have. There are many different colors these pavers come in and most any of them, I think, would work with your neutrals. https://www.homedepot.com/p/Pavestone-Panorama-Demi-3-pc-7-75-in-x-7-75-in-x-2-25-in-Cape-Cod-Blend-Concrete-Paver-240-Pcs-103-Sq-ft-Pallet-36778-CCBL/300999123

There are commercial janitorial products that you sprinkle on,w ait....and sweep up....repeat as needed.....but before I did that, I would saturate the stain with Dawn dish detergent....then scrub and hose down....repeat as needed. Also paint stripper removes oil stains....that I discovered by accident when stripping a piece in the driveway.

As Bruce said, cobblestones aren't supposed to be smooth and even. Unevenness is expected and even desired since it gives it a nice hand made rustic look versus the machine precision of other pavers. But if they are really bad, you have to redo them one by one. You can't tamp down on top of them.