At the present moment I have assumed that a mobile may be a radio receptor, but in bluetooth is a poor transmitter (0 - 1 meter , maximum 10 - 20 meters, samsung J5 I fear 1 meter....)
So the walkie-talkie mobile options are only if you have data.
There is another option with IP or wifi (need data then....).
So the only answer I think is using external walkie-talkies. In fact I have two motorolas . I have charged with the batteries and ready for next wednesday.....
Usually other walkie talkies half duplex are compatible. So another member with other "pair" may be useful.
They have to prepare and disinfect the devices before lend.
P.D. This measure is pending of being approved by the members. I don't understand but there is a lot of fear. I think if I can assure more perhaps is possible. Perhaps using additionally an app like TraceCovid.
Do you know If I can use in Spain and obtain results ?