As a follow up, all computers in our apartment seem to now be able to connect and hold the signal. Nothing really was changed, but it seems to be working alright now, though, the two Linux computers always show a signal strength of below 20%, and often in the single digits, but, it's working, so who am I to complain.
However, I am always curious about tech stuff, and looking to improve things, and something that I have come across is the powerline adapter option. Essentially, you run a cable from the router or modem, to one adapter which plugs into any old wall electrical socket, then you have another adapter which plugs into any electrical socket anywhere else in the house, and you feed a network cable from it to your computer, or another router, or whatever. Basically, it just uses the existing copper in your house as network cable. No new wires to run, and it means a reliable connection anywhere in the house.
Cool concept, and again, if anyone has any personal experience, I would appreciate feedback.