Net assistance setup up a 300 series switch

My internet provider and cable company recently upgrade my system.  My old system setup was cable/modem with built in wireless was hardwire to a Netgear Nighthawk router (two computers hardwired).  The cable modem sent signal to all my TV boxes in my house.

They replaced it with a separate cable modem that is hard wired to a two-port switch which is connected to A Calix 2 router with 2-ports.  The 2 outgoing ports are connected to the EERO and the whole house DVR.  This render my Nighthawk inoperable since it not plugged in they said I can't use my router with the system unless I connect a switch in the system.  The technicians that installed the upgrade did not know how to setup a switch to be able to use my router so I can go back to having two computers hardwired instead of WIFI.  A second technician had to come out the next day as one of my TV would not stay connected to their system.  I asked him about how to go back to a hardwire on my computers while using my router.  He said I would need a switch but did not know how to make the system work.

Looking for possible ways to install the switch and be able to use both my Nighthawk plus the cable company’s Calix router and the EERO and whole house DVR? 

Any advice would be helpful since my cable/internet people are not tech savvy people.  Do I need to call them and get a separate IP address, or can I make this work without slowing down my system (present speed 600 Mbps download and 7 Mbps upload)?

Thanks

Brent