Cleaning Cat Spray?

I created a very comfortable and warm shelter for my 3 ferals. They lived there for almost 3 years. Last winter, another feral from the neighborhood tried to seek shelter there and there was a fight, the feral sprayed in the houses and my ferals sought out new shelter. I've tried cleaning the houses and surrounding areas with a solution I found online called "Anti-ikky poo", I sprayed the houses thoroughly, changed the straw, cleaned the heated beds, and changed the vinyl flap doors, all to no avail.

They still won't go in there! I have to do something for them before the winter, but don't know if I should buy new houses, or relocate my existing ones. I don't know how to resolve this problem. What should I do?

By Alexandra