How to connect two routers with different providers to the same network?

Question

Computer networks

There are two rooms in which a total of 12-15 PCs: in the 1st room there is a router, the Internet comes into it via a 3G / 4G modem from the same router, the cable goes to the hub in the 2nd room forming a common network (there is a network folder from the first room ). There was a problem of lack of Internet for everyone, so the idea arose to put another router with 3G / 4G in the 2nd room.
Actually the question is how to organize a separate Internet, but a common network?
I must say right away that there are no wired providers.

Answer 1

Install Mikrotik. The easiest option.
It is more difficult - the gateway on Linux.