On the site http://www.lavenhamliteraryfestival.co.uk I have just added a second graphic to the header. The original site name and festival date graphic is right aligned in a rich text widget in the header widget area. I added another rich text widget before the original and put the new logo graphic left aligned in there. In the header widget admin area I set the columns to 2, equal height row (not sure if this is necessary) and as an initial guess I set each device type widget widths to 30,70;
It all works fine except that the new logo on the left does not scale on my iPhone X in portrait mode, so it looks far too large relative to the original graphic on the right, which does scale. It looks ok in landscape mode on the phone and also on my laptop.