Hello. Ideally, of course, the hotel would be good to use special equipment in the form of business class access points. Which are designed specifically for such tasks. Powerful and productive. For example, TP-Link EAP115 . Which work roughly like this:
I understand that there is not always such an opportunity.
Let's return to your equipment. With the help of channel settings, width, etc., it is almost impossible to increase the range of the Wi-Fi network! The speed of Wi-Fi can be raised a little by these experiments, but the coverage is unlikely. Although I wrote about this in the article how to strengthen the signal of a Wi-Fi network? We increase the range of Wi-Fi . But it is from the settings of the result that there is practically no result. In your case, install another router on the 4th floor of the hotel and connect it to the second on the LAN. If you use a repeater , as a last resort.
Now about a single Wi-Fi network of several routers and automatic switching between Wi-Fi networks on devices. With the help of conventional routers (Huawei, TP-Link TL-WR841ND, etc.) it is impossible to create a seamless Wi-Fi network. In order for devices to seamlessly switch between these routers quickly and without interruption. The same is with repeaters. The network is like one, but no, the devices will always break the connection when connected to another access point. Much more and on the device (the client) depends.
Therefore, it is generally better to make different SSIDs and one password (for convenience). And it is also desirable on different channels. Or on each router put the channel selection to "Auto". Or with the same network name, but with such painful switching. In any case, the device automatically clings to a Wi-Fi network with stronger signals when moving around the hotel. And this is already good.
I also want to advise you to pay attention to Mesh-systems. Very cool thing. Recently I tested such a system from Tenda - Nova MW6 . It is modular, you can buy as many modules as you need. For example, for each floor. The setting is very simple. Well, there will already be a real seamless Wi-Fi. Now many manufacturers of network equipment produce such Mesh-systems. In the future they will replace conventional routers.