Page Social Image's not showing up on Twitter preview, but works on facebook

I've just helped my friend make this site. I've allocated the 'Social Image' per page in each page's settings. This correct image displays fine when the site is 'shared' on facebook. HOWEVER the problem is that Twitter does not seem to pick the correct image and just grabs a weird section of the first page image which is the page header logo. Is there a way to make Twitter read the site correctly? Do we need a line of custom CSS? Help... I'm not a coder...