One Netcom phone line Two modems

One of my classmates wants to install a network cable, but there is no phone at home, and there is a phone next to it, but it has been connected to the house by another phone line on top of the phone. It has installed Maoer Internet and can access the Internet normally; now I want to ask if it can be used in Then connect another cat to the Internet at the same time? Will the internet speed be faster than using a router?