Imhalfdead :
They have a wifi router connected to fios I'm pretty sure
OK, hold right there. If this is indeed Verizon FiOS, there are other considerations.
I'm assuming they also have TV (and maybe phone) through FiOS? You can't just replace that router. It is the central brain of the whole thing. It supplies the TV boxes with their signal and an IP address. It allows multiroom DVR, etc, etc, etc.
That Verizon supplied router
must be in the chain somewhere.
MoCA.
You do have a few options, though.
1. Where is the router? Hopefully not in the basement. That is the
worst place to propagate a WiFi signal from.
2. Antenna orientation? Sideways? Straight up?
3. Possibly your best option is a
MoCA coax->Ethernet bridge.
Assuming the whole house is wired with coax, and that coax talks back to the main router and settop box, you can plug that coax-ethernet bridge into any coax cable. And then it serves up an ethernet signal from the RJ-45 port.
You can use that for a multiport switch, or a WiFI adapter.
Put it upstairs somewhere...maybe close to the middle of the house. Poof, new wifi signal.