Orbi satellite add-on + internet speed issue

Wow that's a lot of questions, many of which I had no idea how to answer so I did some research.

Firmware: RBR20 is v2.3.5.26 and it says it is up to date.

I have no idea what mfr means and the modem provided by my ISP doesn't diusplay the maker's brand, just the ISP name on top. Here's a couple of photos:

Photo01 

Photo02 

I have tried wiring a laptop to the modem directly but believe it or not, out of the 6 laptops we have at home none has an ethernet port. I have used a cheap USB adapter but the speed only shows close to 100 Mbps so I'm assuming that is the adapter's speed limitation. I will go through the hassle of moving a desktop PC with an ethernet card later today to run some tests.

The house is approx. 240 m² (790 Sq Ft) on 2 levels. The modem and the router are close to the ISP line outlet in the living room downstairs. Two RBS20 satellites are upstaris, one is approximately above the router (around 5m / 16ft away but separated by the floor) and the other is in my home office, apprx. 5M/16ft away from the other satellite (and farther away from the router). They are closer than the recommended distance but considering that the signal has to go through the floor I'm guessing that should be ok? When I try to move it farther away it shows an amber ring instead of a blue one.

I don't know how to check or change the channels that are used, nor do I know what Beamforming, MIMO or WMM are, let alone how to activate these. I haven't seen any "advanced" tab in my Orbi app. I can see that all our mobile devices are connected in 5 GHz but the signal shows orange for most of them, only green for a few that are really close to the router or satellites.

Armor and Circle have never been activated and I don't know how to disable Daisy Chain, Fast Roaming or IPv6.

Has a factory reset and setup from scratch been performed since last FW update? --> Nothing has been done since the gear has been installed by the ISP tech who initially came to intall everything, so I'm guessing the answer is no. The only thing I've done is reboot the devices a few times when the speed was too low.

Based on these answers, would you say adding another satellite is the best solution? I don't mind buying another one, but only if it will help. I'm a little surprised that so many satellites are needed. The house is big but not huge, and it has a roughly cubic shape so there are no hidden corners or weird shapes. It is an old house though (probably around 30-40y old) with concrete walls all around, including the inner walls that separate the rooms. Does this affect the wireless signals?.