RUTX50 would indeed provide a good solution as a mobile failover, considering you have good LTE/5G coverage in your area.
If 5G is not available, RUTX14 could be used instead.
RUTX12 can be considered, as it has two LTE Cat6 modems, thus, the device could be used in load balancing configuration, meaning that all (two mobile and WAN) interfaces are operating at the same time. However, since Cat6 modems separately would not reach sufficient speeds, different camera streams would have to be manually routed through different interfaces and, in wired connection failure case, mobile might not be enough to support stable streams as well. And that is not including possible throughput decrease due to weather conditions or tower loads during more busy hours of the day.
Best regards,