Sharing network through landline?

To answer your specific question, then for practical purposes the answer is NO.

It is theoretically possible to set up a 'dial-up' connection over a landline and do what you want, however, with the complex content of most webpages nowadays, the screen refresh time might be measured in minutes or even hours.

Fifteen years ago in the earlier days of the Internet, I used a dial-up connection to my company's network to access the Internet. At that time, webpages were simple text based affairs, that could be loaded by dial-up in a few seconds at up to 56 kbps (around 5 kBytes/second). However, the speed of broadband has meant that websites now can be, and have become, much more complicated, and dial-up connections are now too slow to be useful.

I hope this helps.

While dial up ISP's could be up to 53 kbps, that is with digital equipment at the ISP. With a regular analog phone line, the best you could do is 33.6 kbps, possibly less depending upon line quality. Even the worst DSL (384 kbps) would be 10 times that, or low end DSL or cable (1500 kbps) would be 44 times that. So while you could possibly access the internet that way, it would not be "broadband" (which is anything faster than dial up).

I did add a 33.6k dial up connection to our Cisco router at our office many years ago before my boss had internet at home. It connected through the 56k frame relay connection to our factory for internet access. But as mentioned, the internet was much simpler then because nobody had a fast connection. The first time I downloaded a CD image on dial up it took 40 hours (ftp resumed download each night for 5 nights)