Hi Red and welcome 
Long story short, there's 2 ways of looking at this.
You can have 2 fixed wireless services with 2 antennas at a cost of whatever it costs to run 2 services a month. ie 2x $70 a month to run one service at home and one in the shed. You have one 'account' but you have to pay for both services, there's no way to 'share' data between the 2 plans and 2 sites.
Alternatively they could set up their own Wi-Fi connection (or even Ethernet but that requires repeaters every 100m) between the Fixed Wireless service in the house and the shearing shed but the setup would be at their own cost here too but I would suspect over a lifetime it would be cheaper to buy a $100 router and maybe a few $100 antennas to broadcast that far so I'd personally be looking down that route. Obviously though if both sites are using the service at the same time then it will share the speed available between the 2 sites (or if one computer is particularly hungry for data it might slow down everything else!) so I guess it comes down to how much speed is needed and how much they're willing to pay for it!
Hope this helps!