How to verify that a multisig address can actually sign a message without leaking info?

I moved all my Bitcoins to multisig (one seed per hardware wallet vendor). But now I face a new problem: quantum attacks. I'm in the 23% of addresses at risk because I did "warm up" my bc1q... (native segwit multisig / P2WSH) address by first sending a few sats and verifying I could then move them.

For I was there in the early days when bogus addresses (but valid) were generated and then people couldn't move their coins anymore. So I learned that lesson and ALWAYS verify that I can indeed sign transactions.

Now as it is multisig I understand there are two secrets to crack, so it's harder than coins on singlesig.

And I made sure to stay underneath the "satoshi wall".

I could find addresses from my multisig wallet by taking the two Zpub and deriving addresses but... Is there a relatively easy way that when the day comes I'll really be able to sign transactions moving the coins without broadcasting any info?

Should I for example use Sparrow in offline mode and see if I can prepare a signed transaction and then use a transaction decoder ? And I'd then be reasonably sure that a) the multisig address instead belongs to me and b) I'll be able to move the coins when comes the day I want to move them?

Or is there a way to run a fake Bitcoin node (using a modified codebase) on my own LAN (not connected to the Internet) and simulate transactions there? Is there an easy way to do that?

Basically: it's a lot of money to me and I'm scared to send coins to an address that hasn't been "warmed up".