“Will 2 routers work on the same phone line same isp?”
Yes you can have 2 router on the same line, BUT you would not be able to use both at the
same time you will have to turn one OFF to use the other one or disconnect the phone
line from the one not being used.
Your ISP modem will not be able to synch with TWO Modem/Routers on the line it will only synch with one at a time