Rounded images and columns

Hello, I state that I am not an expert with the creation of sites.
My problem is with the images and columns of the homepage: I would like to create a homepage with two columns with inside two images with rounded edges.

Not only I can’t round the edges, but when I set the double column it is impossible to see it!

I can see the site in the way I want only when I log into my wordpress account and look at it from there. When I look at it as a visitor the images are huge and square, arranged one per row instead of two as I would like.

I would like to know how I can solve this problem and see the site as I can do when I see preview as creator.

Thanks a lot to those who will help me

The page I need help with: [log in to see the link]