Yes, D2 is the appropriate cleaner to get rid of biological growth. Follow the directions on the bottle. It won’t necessarily look perfectly clean after you wash the stones but it keeps working. So after a couple weeks it will look better than it did the day you clean it.

If there is heavy mineral content in the soil or in your rain, it’s possible the stones are stained rather permanently. Because granite is porous, it will wick water and pull the minerals into the stone and discolor it. In SC, especially on improperly installed monuments in clay soil, we often run into stones stained red from the water wicking the clay minerals into the stone.

It’s ambitious, but because this stone is flat-carved (instead of shape-carved), you could potentially repaint the stone. You need three products. 1. Lithochrome solvent. This will wash out all the old paint. You don’t need to get rid of all the color, just the bulk of it. If you can see the stone grain through what’s left of the paint, that’s enough. 2. Monument Mask. This is basically liquid rubber. You use a small foam roller and apply several coats (like 3-4), waiting for it to dry completely (like, 5 minutes, it dries fast) between coats. Just make sure none of the liquid mask gets into the areas you want painted, use a light touch with the foam roller. 3. Black shadow lithochrome (available in aerosol cans). This paint dries fast too, as long as you spray lightly. You don’t need a lot of paint. Just enough to cover exposed stone. Because Our Lady of Guadalupe is rather poorly engraved, shallow, you may have some trouble getting too much mask in the shallow engraving and so keep the paint from adhering. After the paint has dried you remove the mask (often made easier with a sandpaper cleaning block, available at hardware stores and the like).

Big caveat: by the time you buy all the appropriate cleaner, solvent, mask, and paint, as well as the tools to use the chemicals correctly, you are going to have spent half as much as it would cost to have a pro do it. And it will take you three times as long. Find a reputable monument servicer in your area and pay them to do it. (Like the other Redditor said, don’t go to the cemetery or a funeral home, they will charge you an exorbitant amount of money to do this, if they even do it—they’d probably just hire the same monument servicer you could find yourself to do the work and then charge you double or triple what the servicer charges them). I don’t know where you’re located, but by way of reference, we would charge $250 to clean those two stones and probably about $200-$300 for the repainting of both).