Lost google home network after changes to R7000

Thanks so much for the quick reply.  The Ziply modem is an (Arris?) NVG578LX.  The situation is that the Ziply modem is in a main house, while the NG one is in a separate dwelling.  We are an extended family situation, so keeping the two networks separate isn't super critical, but I think would be nice just to minimize the number of devices one house or the other would have to be concerned about when debugging connectivity issues.  The two buildings are too far apart to share a wireless network, and again, it is desirable to keep them relatively independent of each other.  So, I want to keep the wireless and wired connections at both locations (on both the Ziply and the NG routers).  Right now it is mostly working with the NG configured as an access point with its wifi networks having different SSID than the Ziply.  The primary downsides of this current configuration is that the Google home devices no longer work properly, and the minor downside is that we are no longer on separate networks so the main house can see the auxiliary house, and vice versa.  I haven't tried going through the setup process for the lightbulbs and Google Home speakers, so that may be a viable option.  I did read something somewhere that mentioned making sure that a setting on the router allowed devices connected to see each other, but I didn't see that on the NG router (when it is in AP mode some settings are inaccessible so maybe that is why).  I'm motivated to find an option different from what I have now because I liked what I did before, but just can't remember the right words to find the instructions for what I did.  I think it involved setting up a subnet with the appropriate mask, probably some setting having to do with DHCP, and maybe some port forwarding.  It may have also involved doing something like assigning the NG router a fixed IP address.  Again, I'm really not very knowledgeable about this stuff and I could be misremembering or misusing some words.  I just know I found very easy to follow instructions that enabled me to do what I did without too much trouble.   

What I did before was attractive because it ended up doing what I wanted, but if there is a relatively inexpensive piece of hardware that would facilitate accomplishing what I want, without too much trouble, I'd be open to learning about that.  Would a simple switch a couple of ports let me create the separate network?  If I could use something like that, then maybe putting the NG router as one of the outputs from the switch would be easier than trying to brute force the NG router to work differently than it is primarily designed to do.  The switch idea led me to doing a quick search and finding this:  https://community.netgear.com/t5/Nighthawk-WiFi-Routers/Configure-R7000-as-a-switch/td-p/1470186.  Maybe that is what I did before?  If that is a viable option, then I just need to find more detailed instructions.  However, if a $20 switch would be more plug and play, then that may make more sense.