I have my incoming fibre over copper modem/ router access point in the loft (overhead incoming line), with wired LAN to various points around the place, one of which goes to a second normal modem / router / wireless access point on the ground floor.
Both are 5GHz / 2GHz and all wireless items are configured to access which ever provides the best signal. There is no where in the house or my big garden, where I do not have wireless access. Loft unit is BT Home Hub 5A with its firmware replaced with OPEN WRT, on the ground floor I have a Netgear WNDR3400v2, both on fixed internal IP's. All works a treat and has done since set up.
You just wire a LAN cable from the port of one, to the port of the other, ignoring the WAN (phone line port) of the second unit.