Some onboard graphics card pretty amazing. Like you can even run 3 screens on the newer onboard graphics: 2x digital (1x HDMI + 1x DVI) + 1x VGA.
So you'll need to tell us what ports they have an what their screen requirements are? Like do they want 19" 16:9 monitors with a poor 1366x768 resolution or like 23" with 1920x1080?
There are quite a few older desktop integrated graphics chipsets that can support two screens, but you'll have to check out which ones are already in there and if both connections work at the same time.
Alternatively, fit each one with a cheap discrete GPU and you'll be all set.
Those cheap cards will do the trick and they don't require better power supplies either! Get some DVI-VGA adapters if you're short of a few when opening the boxes and you're all set.