Can we configure 2 routers work side-by-side, as equals?

I neglected to post our modem's info; it's a WebStar DPC2100R2. A quick check found several online descriptions, and none mentioned a routing capability.  (But several did mention hooking them up to a router.;-)  So I guess that's a bit more evidence that our Orbi thingie is getting a plain single-public-address IP packet stream.  

Actually, one diagram shows hooking it up to a splitter, with one going to a TV set and the other going to a "router".  Some people do still have analog TVs, I guess.  My wife, who has a gang of old-movie-fanatic friends over occasionally, has a big-screen Roku, but it's a digital tv.  Yesterday she got it working with the Orbi's wifi, and says it works better than it did with the old Apple Airport Extreme, which occasionally lost the connection, and had to turned off and back on to get it working again. She says that doesn't happen now.

But that's not related to my problem, of getting my web server(s) back online.  The main one is a little linux box, which the Orbi finds in its Wired list and calls "Asus".  But the Orbi still won't pass any incoming connections to it.

I also have web servers running on 2 Macbooks, used for testing new stuff. They and the Linux server are talking to each other via the Orbi, and can see each other's web servers.  But nobody in the outside world can connect to any of them.  The Orbi shows all 3 in its device list, with correct names and addresses, but the web servers only connect if I type their IP addresses rather than their names.  I wonder if that has anything to do with the problem with connections from the outside world?  

One of my next tests is to tell the Orbi to forward port 80 to one of the Macbooks, and see if my "outsider" cellphone can reach it.