All looks good, dcdiag is clean. The only issues I see
On DC1 add server's own static address (192.168.200.15) listed for DNS, then do ipconfig /flushdns, ipconfig /registerdns, restart the netlogon service
On DC2 add server's own static address (192.168.200.14) listed for DNS, then do ipconfig /flushdns, ipconfig /registerdns, restart the netlogon service
On DC3 add server's own static address (192.168.200.50) listed for DNS, then do ipconfig /flushdns, ipconfig /registerdns, restart the netlogon service
and also confirm from PowerShell
Test-ComputerSecureChannel
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