Do I need a new router or a better internet plan

Hi, I live in a 4-floor house (1 floor is the basement) 6 family members live here our internet is slow. Our modem is on the 1st floor and I also have a 3 piece Eero wifi pack. My current plan is up to 100mbps download, and 10 Mbps upload. After talking to a cox tech support they say that it supports 5-7 devices. I will list the devices that are connected down below if it matters.

Device rundown(I added everything that connects to the WiFi):

3 PS4 game consoles

1 Xbox One

2 Apple TVs

1 Smart TV

6 iPhones

7 Computers(One streams music constantly because we have a radio station.)

3 iPads 

2 Homepods

3 apple watches

Smartlights

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