Then what to do with the spare routers. Not possible to use it as repeaters? Please suggest. Going on tight budget. Can't afford another device right now...
Maybe but it depends on the router. Does it have the ability to run in repeater mode. If it does not have that feature then you need different hardware.
So the first step is take some device like a phone and see how much signal you get outside the house, and then again inside the remote house. There is no magic wifi device that will get a signal that does not exist.
A repeater needs to be able to get a strong signal from the first house and still be able to send it to the second house. Lets say this was a big open field. You could place a repeater 1/2 between the main router and the remote device to extend the distance signal goes.
Obviously you can't just mount a router out in the middle of the yard between the 2 houses, you would have to get at least power there and home routers don't do so well in the rain.
So if you get ok signal outside the remote house but not inside you might try to place a router/repeater in a window on that side of the house and see if it works. If you have poor signal even outside the house you might be able to place a device in a window of the first house.
The real solution is to place special outdoor equipment on both houses but of course you would have to spend money. Likely be about $100 for a pair of outdoor bridges.