bfastmag images not responsive to devices

http://www.life4u.org.nz
Your theme does not resize home page grid images accordingly to whatever device or screen size it is being viewed in.
It is totally unresponsive.
when viewing home page in a desktop its fine.
then when I start test shrinking the browser window, images can only keep integrity up to a certain point, then images become distorted the narrower you go in. You dont have to know what mobile phone it is doing this in, because I have tested many phones and in the computer it is plain to see when you shrink the screen browser.
I have resized all my site images and they are fine in the full width desktop browser.
But in a Samsung 7 phone, all I get is the squeezed in narrow version.
The two images I have attached, all you need to do is shrink the browser to narrower size, and you will see that the browser does not keep the integrity of the images.
Your helpdesk told me: Use the Image like 700 x 340px.. or Keep the Aspect ratio like this. The Featured Image will work.
In the desktop grid, the big pic is fine, but the smaller ones are stretched.
In a mobile, everything is squeezed narrower.
In previous emails to support I have provided my login so they could investigte further but I dont know where to put these details now, nor how to attach the screenshots.
Thanks
Gillian