Outbound policys?

Hello.

I new problem has come up with my cellular service at home.
I have MBX 5G with 2 AT&T unlimited 5G sims and one MTD with 1 non-5G Verizon sim. The MTD is a WAN connection to the MBX where all three WANs are managed.
The performance of the AT&T connections is by far better than Verizon, however

Problem: Recently, AT&T is frequently performing maintenance on the line-of-sight tower that I connect the MBX to. It’s hopefully to improve the signal and block sizes of there 5G antennas.
When this occurs, the bandwith drops to between 1-2Mbs, the latency increases, BUT the signal parameters remains strong.
I would like some help with an outbound policy that can fail my AT&T WANs over to my Verizon WAN when this occurs.
I’m not sure if it’s as simple as specifying “Fastest Response” or “Lowest Latency” as the algorithm used in a policy but I’d like to be more specific to say if/when AT&T download bandwidth is <30, then failover.
My router runs a house with 35 devices so keeping the highest bandwidth of the three WAN connections is optimal.
Any advice in how to accomplish this will be much appreciated.

I also have another strange problem. Both of my AT&T sims are unlimited Business plan 5g sims. BUT, I cannot get both of them to connect to 5G simultaneously in my MBX. Each of them connects to 5G when they are the only AT&T sim in the router, but only ONE will connect to 5G when both of them are present. Is the tower doing this? I find this strange and annoying. I have not called AT&T yet but will after some more research.

Thank you.