Electrical – Adding 2 X GFCIs to protect Switched and Unswitched Hot sharing same Neutral and Ground

There is no problem with this. In fact it's very common, especially when wiring ceiling fans. The power (2 wire /w ground) enters the switch box, then a switched hot and unswitched hot are supplied to the fan (3 wire /w ground). This allows the light to be toggled by the wall switch, while the fan is toggled by the switch on the fixture. It's also a common practice to wire duplex receptacles this way, where one half of the device is always powered and the other half is controlled by a switch (in which case the tab separating the two halves should be removed on the ungrounded (hot) side).

The grounded (neutral) conductor will carry the combined current of the two ungrounded (hot) conductors, so any inductive coupling will still be canceled out. Since the circuit is protected by an overcurrent device (circuit breaker/fuse), there is no way to overload the grounded (neutral) conductor. The current on the ungrounded (hot) conductors will be limited by the overcurrent device, so too much current should never flow on the neutral.

Ground-fault circuit interrupters (GFCI) work by looking for imbalances between the ungrounded (hot), and grounded (neutral) conductors. A grounding conductor is not required for a GFCI device to detect ground-faults. Any devices connected to the Load side of the GFCI device, are GFCI protected. This blog post might help you understand how GFCI devices work.

If you take a look at the code quoted in this answer, you'll see that not only are the "No Equipment Ground", and "GFCI Protected" labels required. You should also not connect any grounding conductors to any 3-prong receptacles that are downstream. If there is no grounding conductor in the circuit, no grounding conductors should be connected anywhere in the circuit.

Also of note, is that this only applies to existing circuits that were installed before the code change. All new circuits must meet or exceed current codes.