Can't print to shared printers between 2 Windows 7 computers

I've set up the Homegroup, and all appears to be working. I added in my laptop as well. My laptop can print to both of the printers, so my hopes were raised. BUT...I still can't print to my wife's printer, and she can't print to mine. I've deleted and added the printers back in (by "finding" them in control panel) but it makes no difference. My pc will only print to my attached printer, and she can only print to her attached printer. And yet the laptop can print to either.
When I press "print" to print to her printer,the document seems to disappear - when I go to control panel I can see her printer, and there's nothing in the document queue.

Just a thought - is there any real need for two printers? The only reason I ask is that I'm just wondering if you're getting problems because Windows will only recognise one of the printers as the default one i.e. the one you specify.

Why not just use one printer and share that one.

I've tried deleting the CLP310 as a local printer, leaving only the ON BLACKMATT version. It doesn't help. I can't print to it, although my laptop can.
The reason I have 2 printers is that one is a black and white laser, and the other is colour. I'd like both competers to be able to use the colour printer occasionally, but the black and white laser ought to be the default printer for day to day office printing.
The 2 PC's are next to each other, so I could simply unplug printer from 1 PC and plug in to the other, but it's not very elegant. And I know my wife will panic at thought of unplugging USB cables!

Both Samsung, but one is colour and one is b/w, with different model numbers. b/w 210 printer is USB attached to my pc, and the colour 310 is usb attached to my wife's pc. She can use hers, I can use mine, the wireless laptop can use both.