Looks like it's not "5 static IP addresses on 5 devices behind DSL modem in Bridge Mode", but 5 addresses behind PPPoE. If so, you need only one PPPoE connection on one of the routers (1), also ...

How to Configure a D-Link Switch for a Static IP Address. When a network router doesn't have enough network ports to connect all the necessary devices, a switch can be used to add additional ports.

This setting makes IP address related fields available. Type a specific IP address in the IP address field. This address will depend on the starting IP address specified under Setup in your router.

Also: How to change your IP address, why you'd want to - and when you shouldn't To get around that issue, you must know how to configure your router so that it is limited to, say, 192.168.1.1 to ...

This short tutorial walks you through the process of changing a CentOS ethernet interface from DHCP to static--but be prepared to type.

To configure a static IP address on a Red Hat system, let’s start by listing NetworkManager’s connection. The nmcli command shown below will list network connections and devices on the system.

What you see in that sample file is all you need to configure that static IP address. Do notice, you aren’t setting the address is the same fashion as you did with Ubuntu 16.04.

Devices with static IPs can coexist peacefully on a network where DHCP is present, as long as the DHCP server doesn't try to hand out the same address you are manually assigning.