No, it wont work.
See, the line will only support one modem. Its not quite like Ethernet.
You might look into getting a new router... what router do you have right now?
Make sure your router is in a central location of your home... Preferably at head height on the first floor.
Is the connection weak, or just not there at all? I wouldent really say another router is needed unless the connection is below 50%.
EDIT: You might also make sure the antenna is facing directly up.