Multiple nat routers may cause a issue.
You can't really turn off NAT in a consumer router. Your only option is to in effect remove the second router. You would have to use the second router as AP but if you needed firewall features or other option you will lose all that.
You might make it work by defining the second router to be in the DMZ of the first. You might also get it to work by port mapping ports from the first router to the second.
Running 2 routers is never a good idea but I know there are many cases where the ISP provided router is garbage and you have no option to remove or bridge it.