Two DSL line, Backup line and Dinamic DNS

XG Firewall.

I will have two internet line, one primary anda a secondary line used for backup line.

The primary line have a Static IP for my services. eg: 111.111.111.111

The secondary line have too an Static IP eg: 222.222.222.222

If the primaty line fail the backup line (secondary line) must replace the primary line; and i know that that is possibile.
But, i have service in my lan (web server, mail server, and other) that work with an external DNS 3&***; level, eg: webserver.xyz.com and mailserver.xyz.com.

The DNS provider is configured with an A record that use the Static IP of Primary Line: example: record A : webaserver.xyz.com : 1111.1111.1111.1111

when the primary line fail, the dns name webserver.xyz.com point again to 111.111.111.111 instead of 222.222.222.222, and this is A BIG PROBLEM.

Is there a solution?

I figured this, by using the DynemicDNS feature (sophos provider) to:
1) the external DNS is configured with a redirect webserver.xyz.com -> webserver.myfirewall.co
2) configure the XG Firewall Dinamic DNS to swap the dinamic DNS webserver.xyz.com from 111.111.111.111 (Primary Line) to 222.222.222.222 (Secondary Line) when the primary line fail.
Is it possible?

Thank to everybody

Ettore