Without local access this will be difficult if not impossible to achieve.
You are experiencing a split-brain scenario where both units 'fight' for forwarding traffic.
For a separated cluster (same wan and lan IPs), you can't have 2 different IPs for management. Your best chance is to first get the cluster back online, by setting up the HA parameters as described above. This way you will stabilize the network and can further make changes.
Once the HA cluster is stable you will be able to enable dedicated management interfaces, and then change the IPs for these management interfaces.
- Toss a 'Like' to your fixxer, oh Valley of Plenty! and chose the solution, too00oo -