Orbi in AP mode

People can give more detailed advice if you identify the brand and model of modem & router that you have.

(Sort of guessing this is AT&T service, but "who knows"?)

The Orbi can certainly be set to the same SSID and password as the ISP WiFi system, but they will not "integrate".  If the Orbi is configured as an Access Point (AP), then the ISP router will assign all network addresses.  Devices will connect to whichever AP seems to offer the best service.  The two WiFi networks will, of course, be interfering with each other, but that may not be a serious problem.  For devices fixed in place this may be OK.

For devices that move, such as mobile phones, tablets, laptops, this could be "not good".  With a single mesh network (Orbi, Linksys, Google, whatever) when a device moves closer to a better AP, it usually switches and the switch is coordinated with the mesh system.  With two different WiFi networks having the same SSID and password, there will not be any coordination.  I have no idea what will happen.  My guess is that the phone (for example) will stubbornly stick with the original AP as the signal gets worse and worse until it finally drops.  Only then would it look around again.

Orbi has VLAN capability which is specifically designed to accomodate network TV service.  So, the ISP router may not be required.  If you provide some more details, some of the smart users may have solutions for you.