Stories grid thumbnails wrong dimensions

please see our homepage here: http://longreads.oneworld.nl/

The thumbnail dimensions are not right after the 6th thumbnail.

Also: the new stories appear on the bottom. Is there a way to make them appear at the top?

Thank you!