You may consider other options than PowerLine too, I have been using for almost 3 years 2 set of LinkSys PLSK400 adapters to transfer ethernet signal over a 3-stories house since I also had no option for additional (UTP) wiring. Initially it was meant to transfer IP signal for Interactive TV's but one certain thing is that the electrical wiring can still mess up your plan.
It is very important that you also avoid electrical junction boxes and connect the Powerline adapters directly to the wall outlet. Even that is nat a guarantee you get the best performance, in my case few outlets were exreremly slow: 1.5MB/s for upload while I had a 40MP/s Internet subscription. I was told that these adapters perform the best only if the outlets (and corresponding wiring) were installed on the same circuit which absolutely was not in my case. In my house there I have up to 7 different circuits/switches ...
Anyway, after a lot of trial/error I found a few suitable outlets for connecting these adapters still speed was not optimal. Also you have a risk of adapters getting confused (since I had 4x at home) and needed occasionally to reset them. It is hell of pain when you're watching TV and in the middle of some interesting movie scene you have to come downstairs just to reset the main adapter )-:
The worst part started when I tried to uses these adapters for transmitting video of my IP-camera's: extremely slow netwrok speed, a hell off dropped frames, freezing recorded motions, ...
I solved most of issues by adding other type of adapter to my home network: 3x MoCA switches. These type of switches use coaxial wiring to transfer both TV and Ethernet signal in your house, which are 2 or 3 times more expensive than PowerLine adapters but based on my experience are much faster and much more stable for RTSP (also much less packages being dropped).
I am using now one of my PowerLine sets to transfer data from 3 IP camera's and use 3x MoCa switches (Hirschmann moka 32) for 2 other IP-cams including TV signal for 2 rooms plus connecting 2 PC's and 2 laptops at home. I see in one of your photo's a TV bracket on wall, you may also consider MoCA switch for your wiring there!