Images pixelated at larger dimension?

Site URL: https://www.macdonaldphoto.com/

I am working on a website and for some reason, we keep having problems with our image being pixelated even at a higher dimension. I have attached photos of the images so you can see the difference in the pixels and also attached the settings they are being exported with. The pixelation is not there at 1500px on the long side, but reappears when resized to 2000px or 2500px. We would leave them at 1500px, but the images are not as crisp. Any ideas on what is causing this? 

Not sure if you can see it on the pictures of the blue house (it's in the sky), but I have attached screen shots of other images with this strange pixelation pattern. Which can be seen in the ceiling of the other rooms I posted. 

I just looked at everything in Safari and it looks great. No pixelation.

@sayreambrosio This screenshot is in safari--it's still there unfortunately.

2 hours ago, klberg said:

@sayreambrosio This screenshot is in safari--it's still there unfortunately.

You have some super good vision. I never would have noticed it without zooming in super big.