How is the OpenWrt router at house 2 connected to the ISP router? Is it LAN - LAN, or LAN - WAN?
How are the hosts at house 2 connected to the network? Do they connect directly to the OpenWrt router (on a unique subnet), or are they connecting to the ISP router?
Please include the beginning... it is relevant to the configuration and troubleshooting.
Remove the listen port on the interface definition (since this is 'client' mode).
These don't do anything on OpenWrt. You'll need to specify this in the dnsmasq config... this can be a bit annoying, actually... see this thread.