Trying to diagnose wireless problems remotely, and with only patchy non-technical descriptions is a bit of a non-starter. The best any of us can do is tell you the pros and cons of the various solutions.
For example, you said your "Internet speed" has dropped by half in the living room since installing what I think might be a TP-Link extender that spell-check has changed to top-link. That could be because your devices in the living room are picking up a stronger signal from the TP-Link than your home router. If you recall, I said that repeaters/extenders will often have the effect of reducing the wireless speeds. That seems to be exactly what you're experiencing.
If you're non-technical then you're going to have a hard time setting anything up so that fixes your camera problem without knackering the rest of the house Wi-Fi or wasting time and money. Just chucking money at the problem without some understanding of what's going on behind the scenes ain't going to work.
This is one of the big drawbacks of wireless. It's seen as easy and convenient, which I totally understand. But in reality it's like building on poor foundations; sooner or later the cracks start to show. We've got so much gear relying on wireless such as smart heating, music streaming, smart phones/tablets/laptops, security cams, cordless home phones, office peripherals, games consoles, smart TVs/BD players/streamers etc. Then there's the overlap from neighbours wireless systems and sources of wireless interference in out own homes such as the 2.4GHz bleed from microwave ovens when running. It's all a big wobbly pile of tech.
The reason it looks like things work seamlessly is often because a connected device holds a little reservoir of data to help cope with the breaks in service. For some activities this is fine and it helps paper over the cracks. However, for something like a live streaming application such as your wireless camera you're seeing the feed live, so any service drops become noticeable pretty quickly.
Anyone who promises an easy solution to this either doesn't understand the problems well enough or is just trying to flog a bit of hardware regardless of whether it fixes anything or makes things worse, so beware Greeks bearing gifts.
If money isn't an issue, and you want this doing properly then have a look around for your local data network specialists. You want someone who can do a proper wireless survey, preferably with some data logging gear that can read what's happening over a 24-48 hour period. They should also take an inventory of the gear you own to weigh up its capabilities and requirements. Once the results are in, then they'll put together a custom solution for you. This will involve a mix setting your existing gear up and some changes in hardware plus some hardwiring of repeaters to fill in the wireless dead spots.
Where money is tighter but you have the luxury of time then you can go the DIY route. You'll need to do a lot of background reading to get your knowledge level up.
Where your router is ISP supplied then nine-times-out-of-10 it'll be a very basic device, so changing to something better is the first step in getting a better performing system. You want a Router such as a Netgear Nighthawk or similar that can run both 2.4GHz b/g/n and 5GHz ac as separate layers (dual band), and that also supports Mu-MIMO and beamforming.
After that, wired Ethernet connections to range extenders (Mesh or simpler wireless ac devices) that also support dual band use. Depending on what you're trying to run, you might benefit from having the 2.4GHz connection set up as a separate Wi-Fi name so that it doesn't have to share network connections with other 2.4GHz devices in your home network.
If you can, and if the camera supports it, run the Ethernet cable direct to your router. That will solve everything related to the camera issue.
