Not easily – you could opt for a quad video processor which would display 4 separate video images on the screen; these can be bought fairly cheaply.
To achieve two images on one screen, you could consider a video mixer, but it would either show a picture within a picture – or half of each picture, adjacent to the other – with a vertical split. To achieve this, video mixers have to sync the time-base of each video signal, which means that they are not cheap.
You might be able to pick one up cheap on ebay – but I reckon this will sell at over £100.
http://www.ebay.co.uk/itm/Edirol-LVS-400-Video-Mixer-Live-Switcher-Vision-Mixer-4-Channel-/261196499078?pt=UK_Video_Broadcasting_Equipment&hash=item3cd0864886