Yes you can charge 2 devices in parallel, each plate has 12W Fastcharge 2.0 (incl. power supply 25W).
Galaxy S10/S10+/Buds/Watch and other devices supported, devices that do not have Fast Charge will simply charge slower.

should actually work, since you can at least charge the phone on the part intended for the watch. Strangely enough, it does not work vice versa to charge the watch on the pad for the phone...