2 Routers on Mac-Mini Configuration-Help

I have researched this extensively and getting very close to success but still a network novice and need some help.

I have a mac mini and trying to use a DSL wireless router connected via ethernet for internet access and a linksys wireless router connected to security cameras accessed via airport. The configuration works fine independently but I cannot access the linksys router when the ethernet is on. Currently, I have changed the routers ip addresses so they are different. I have the IPv4 set on both the ethernet and airport to using DHCP and their ip address is the same. I have tried to configure the Airport manually and have changed the IPv4 address but didn't solve the problem. I've changed the service order and currently have ethernet first. Tried Airport first but no success. I've looked at some of the other tabs under network preferences and they go beyond my ability level so haven't changed from defaults. I feel like I am very close but reluctant to start guessing about any other settings.

Can I configure airport manually to eliminate conflict with ethernet and access cameras by entering ip address to camera while ethernet is connected? I can access the linksys router and cameras via airport with no problem with ethernet off. I have the dsl wireless router to allow other computers in the house to access the internet and this works fine.

If I do have to configure airport manually can you advise everything that would need to be changed. Any advise is greatly appreciated.

the MacMini will always use the fastest Link, in this case the Ethernet.

You have to connect the 2 routers into a single logical network.

On a Tower or Xserve you can have 2 ethernet ports but it still takes significant setup.