Hi, the best way is by getting a wifi extender. That wifi extender will connect to your router and expand the wifi connection, now if you want to use an ARRIS device I can recommend the mAX routers with a coverage up to 3000 sq ft

how far are these buildings away? 

Extenders work great but have a limited distance to maintain speeds. 

A point to point system might be better depending on the distances we’re talking about. 

The other building is approximately 80-100 yards away.  I was thinking of trying an outside antenna.  I also saw some extenders that cover 12,000 square feet.  

I have an ARRIS SBG6950AC2 cable modem/router.  I tried to hookup an Orbi system but I couldn’t get it to work.  I put my modem in bridge mode and followed instructions given to me but to no avail.

Extenders and routes broadcast omnidirectional (in a sphere/circle) So 12000sq ft is only a circle that is 123 ft. Its not going to reach as far as you want it. 

Its why a point to point system would be a better option to connect the buildings. Then you could connect the orbi satellites to the point to point system for coverage in the buildings. 

In terms of connecting the orbi to the SBG, put the SBG back in router mode (disable its wifi) and connect the orbi to it with the orbi in AP (access point) mode. 

Thank you for the information.  So, do you think an orbi router and satellite with a 6000 ft range would cover the distance?  In your opinion, would they mesh at that distance, (80 yards), Or should I just go with a point to point system?  Right now I can pick up enough signal from just my ARRIS router/modem in the upstairs of the building to run a ROKU TV but not enough signal downstairs in the building to run one.  (It’s a vacation rental and I’m trying to avoid another internet service charge.)

Again, thank you for your input.

I don’t think you can do it with one system. 

I think you need a point to point system to connect the 2x buildings and then a mesh system as the point to point functions basically as a wireless ethernet connection. You’re not able to connect wireless devices to it. Thats where the mesh system comes in. You user router +satellites with a set of satellites in the 2nd building. then everything integrates. 

Or if you don’t want it integrating, then use a different mesh/router setup in the 2nd building.