Splitting two silvers *should* only matter if only one seat is available up front. Don't see any other upside. It doesn't hurt though. I'd split them and see what happens. If you only end up with one upgrade, you should not have a hard time swapping your first class seat with whomever is sitting next to your bride in coach so you can sit with her (if you want to).

To split your itineraries, call up CO and ask to have the PNR split. It will work best if you have your original confirmation handy. One passenger will remain on the existing PNR and the other will be assigned a new PNR. If you want to pull this new PNR up on CO.com and add it to your profile, you will also need to have the agent assign a new "itinerary number". Otherwise the website won't let you pull it up. A call to co.com support will probably be the best way to go about this whole process since they're used to doing it. One caveat: You'll most probably lose existing seat assignments, but should be able to get them back if you act quickly online or just ask the agent to do it on the same call.

Hope this helps.