For some context, there are

• 4 pink cables. These are all CAT 5E cables, with RJ45 jacks. The four are named: DEMARC, Family Room, Room Room, & Master Bedroom.
• 4 white cables. These are all coaxial cables (with the copper wire protruding). The four are also named: DEMARC, Family Room, Game Room, & Master Bedroom.

Currently, the ‘DEMARC coaxial cable’ is connected to the ‘Family Room coaxial cable’ and the combo router (NETGEAR router + modem) in the Family Room is connected on the other end using another coaxial cable running from the wall to the combo router (which is on the first floor).

There is good internet connection on the first floor, but it utterly sucks on the second floor.

I got a WiFi extender and I put it half way between the first floor and second floor, but it’s useless. It doesn’t help at all. The speed on the first floor for the 5GHz WiFi is about 400 gbps, but by the time it gets to the stairs, it about 20gbps.

I plan to utilize the wired connection for max. network. What’s the best way to optimize this? I did some research on how a networking switch would help here, but I’m not sure where to put the combo router to optimize it - the aim is such that there’ll still be good network on the first floor for visitors and good network on the second floor as well (for gaming & WFH).