Thanks for the quick reply, Mac. However, the problem would seem to be with the phones rather than Microsoft. I've tried the same exercise with an iPad. The iPad recognises both phones, but the connection repeatedly drops out after maybe one or two seconds. (On the Bluetooth page, the phone shows as 'not connected'. Press/swipe on that, it shows 'connected' for one or two seconds, then 'not connected'.
Perhaps my phones are too old and therefore not compatible with Win8 or ipads? Are there software updates available for old Nokias to make them compatible with iPads and Win8? I'll take a look on the Nokia site.