2 internet on 1 PC?

Question

Computer networks

According to the working need, they brought out the 2nd line of the Internet, on 3 PCs.
The entire local network and two rides are connected to the 1st line.
How can I implement Internet access for these 3 PCs, on line 2 and LAN on line 1, and avoid conflicts between the Internets.
If you have to write a lot to answer, then I will be grateful if you provide a link to the source where there is a solution.

Answer 1

Understandable in the question is much less than incomprehensible. But still, if I understand your idea - buy an additional network card for each computer. Assign different addressing to each network card. On the Internet map - register the gateway, on the map for the local area - do not register.

Answer 2

https://linkmeup.ru/sdsm
start there

Answer 3

register routes on a PC
sdsm

Answer 4

Buy a dual-wan router (it can work with several Internet channels out of the box, either reserving one of them in case the main one fails, or aggregates both channels)