So as to your specific questions about wifi camera's and what you should do, well, it comes down to simply trying the device and seeing if it is in range with high enough bandwidth. If it isn't, the next step is to try adjusting existing antenna on you wireless access point to see if you can get better coverage, as well as check to see how many other people are using the same wireless channels you are using and attempt to get onto a clear channel (hard to do now with the newer standards using three channels simultaneously in the 2.4ghz band when there are only 3 channels that can be used that do not overlap with each other, so everyone uses the same 3 channels (in the USA that is)).
If you still do not have coverage, you might have some options depending on your wifi router to change the antenna's in use (not all will support this, and in many cases to really do this you will also need to be able to control other parameters such as transmit power). You will need to do some research into your wifi router/access point to figure out if it is possible, and what other things need to be considered (such as the use of beam forming, and even mu-mimo as you might not have the correct hardware antennas to support those functions).
That all being said, if the above does not let you connect to the wifi cameras in the locations you have installed them, you will then need to consider setting up additional access points to extend your range. I always recommend using hard wired access points and not using "mesh" networking. The "mesh" devices will just use up more of the limited wifi bandwidth that you have available to deal with repeating the data across the wifi network to the other mesh devices. It "can" be useful when you can't run a wire, but it is not otherwise recommended (if there was additional, dedicated wireless spectrum that is not shared for wifi usage that could provide the mesh network links, this would be a more useful tool, but the reality is that the bandwidth would still be better off as merged into overall wifi spectrum).
For figuring out where you need or should place your additional wifi access points, the best method is to simply test it before having the wires pulled by just using a 50m cable that you just run inside the house through doorways/up or down stairs etc., to see where placing that second or third access point will provide coverage the cameras. Alternatively, look into replacing the wifi camera with a wired one and run a wire to them (obviously not easy for cameras that are around a property and away from the house itself).