HA confusion

[coatmaker618]

I have two physical OPNSense boxes I'm using as my primary router, and either one of them performs fine.  However I have a few problems when I try to run them together in High Availability:

• The network has multiple VLANs (or OPT networks if you prefer), and OPNsense is the DHCP server & DNS server for these networks.  When both boxes are connected I am seeing DHCP conflicts, DNS conflicts, etc. How do I get them to share the info rather than both try to act as the primary router on the network? Is there a config or setting I'm missing somewhere?
• I am on a residential network, so I only have 1 WAN IP & 1 physical RJ45 port for my WAN connection.  How do I keep two (or more) nodes of a HA "cluster"? Do I need to physically move a cable?  Can I create a 2nd route through the "other" routers? Any suggestions are welcome!

PS: Is "cluster" even the right word for HA OPNSense? It seems like it's more of a train, per this post:
https://forum.opnsense.org/index.php?topic=30225.msg146197#msg146197