Combining 3 buildings networks, each with their own internet

As the subject says, I have 3 buildings in a straight line. Each one a 1/4 mile from the other, with the main building being in the center.
It is open air without obstructions between, so I am probably going to at least experiment with long ranged WiFi, to avoid the cost of fiber and terminations.

Thoughts on that so far?

Most importantly though, I am questioning, how to accomplish tying these 3 networks together to achieve a singular network, while either being able to have their own internet, or globally haring the internet? No one location has enough bandwidth to cover all three buildings.