Netgear N600 WiFi Cable Modem Router Model C3700

I have a Netgear Cable Modem Router that I bought in 2013 or 2014.  It really hasn't served me well.  I bought it to replace the cable company's inorder to save the monthly cost of theirs.  I have tried to connect my Samsung Smart TV to the device over WiFi, but I have at least 3 walls to go through and my TV can't connect over the WiFi network to my source, a computer.  I have 2050 Square feet, but I have the modem/router at the furthest point on one side of the house, and connect to the TV at the furthest (diagonally) place on the other side.  I have a second router that I tried to wpa pair to the the main router, and it does allow the TV to connect, but in viewing a movie over the network, it keeps stopping (a rotating circle indicating its downloading).  After a few seconds, the program will start again, but this happens quite often.  I am wondering if there are newer router/modems on the market that provide a stronger WiFi signal, as this is what I'm guessing is the problem.  Does anyone have a suggestion or idea how I can wirelessly connect my Smart TV to my computer without the constant interruptions?  I am not that technically inclined, and it took me a couple of months to even get the things working at all.  I need the device at my computer to connect the cable to my computer for internet service.  I actually have several smart TVs, but I can only get one to even connect at all.  So I don't know how to program the router to accept the others.  Connecting the router/modem to the TV using a wire is out of the question.  The computer and modem/router are in one room and the TVs are all in different rooms throughout the house.  I also have another problem with the router in that when I was trying to set it up, I accidentally created 2 or 3 different networks and now can't get rid of them.  I guess part of my problem is getting the router to allow the TVs to get through to the computer, and the other one is the additional networks I cant use that fill up the channels.  I know this is a lot, but I'm an old fart and technology has long passed me by.