Hey Randy,
If the first stage freezes (yucko)
Yes, all units I have dove have usually a primary port and two accessory ports.
The accessory ports can be used for communications, surface valve or extra regulators.
For second breathing sources we usually use a slide stop to keep the gas from entering into the breathing loop. This is mainly if the secondary gas is a decompression breathing gas.
The only thing to watch for is if the front of the mask has an oral cup for breathing or if the regulator actually comes through and you are using the regulator into your mouth.
This is very important because the side (extra) regulators will not have a direct feed into your mouth and Co2 can build up in the oral cup area. However, it can stop you from removing the mask underwater.
Most people hang a second stage around their neck for bailout if they are not using an extra port. In your situation you would want the second stage to be run from a secondary air supply.
Scubapro has the cheapest FFM mask, but the Drager FFM seems very popular.
A lot depends on design and cost.
If you are looking at this I would talk to Ocean Technology, they have just brought out the new Guardian FFM. Plus, they sell to military and commerical.
link-
Underwater Communications by Ocean Technology Systems, Buddy Phone, Aquacom, Scubacom, Buddy Line, full face mask, AGA.
I currently have a OTS MKI mask that I am rebuilding to dive underwater.
Hope that your family is well Randy.
Regards, Andrew