Statler Brothers Video from the early 90’s. Could this be real for three mobile calls to be made from their bus at the same time?
Maybe they were all talking to each other on a closed circuit
Why not, if they were willing to pay for it? Car phones were a thing from the 60s on, they were common on TV shows in the 70s. They were very expensive and only really used by people who needed them - one was a TV show about a vet looking after a zoo and he had a phone in the car, so he could be contacted in emergencies, high call costs are nothing, when you could lose an expensive animal…
So, by the late 80s, the technology had moved on and putting multiple receivers into a vehicle wouldn’t have been a problem, just expensive, or as @knewman says, it might have been a conference circuit.