Trying to help someone leverage two circuits for terrible uptimes in the area.

I have a family friend who is a plastic surgeon and the building they are in has extremely unreliable comcast. I am trying to pinpoint the root cause but the other professionals in that building also complain. My daughter split open her chin and the ER didn't do such a great job, he fixed it up and I paid nothing.

I am mostly Cisco so I need some help as the Cisco solutions to bring in 500Mbps to 1Gbps connections are going to be expensive and noisy.

My goal is an easy to setup head end that can use Comcast and possibly AT&T (I am open to cellular backups, but I worry about coverage within the building) and then some better WiFi device(s) than the Comcast all in one. I would like fanless devices if possible or those that are quiet.

The office is maybe 1500sq ft. about 5 exam rooms, the doctors office, lobby and a receptionist and imaging/record storage area.