Thanks for the reply!
Can I only use my phone offline when I do the transaction or does it have to be a device that never connects to the internet? And does it matter which device will be offline, does it have to be the first wallet created or does it not matter? Because my computer always is online and I would like to use my phone but it is the second wallet.
I wish all the best!

1. It’s generally recommended to keep at least one of the devices used for multisig offline. To sign transactions offline, you would typically generate the transaction on the online device and transfer it securely (e.g., via QR code or USB) to the offline device for signing. The signed transaction can then be transferred back to the online device for broadcasting to the network.

2. Depending on the specific implementation of your multisig wallet, it is indeed possible to send funds with only one signature, even if you have set it up as 2 out of 2. This flexibility allows for scenarios where one device may be unavailable or lost. However, it’s important to understand the implications of this setup. With only one signature required, if one of your devices is compromised, the attacker could potentially access and spend your funds. Ideally, you should strive to have both signatures whenever possible to maintain the security benefits of multisig.

3. Ledger Nano devices generally support multisig setups. YOu can connect Ledger with Electrum for multisig functionality. You can use your Ledger Nano as one of the signatories, which adds an additional layer of security to your multisig setup. Transactions would require both the Ledger Nano’s signature and the signature from the other device / wallet.

Remember, it’s crucial to thoroughly research and understand the specific implementation and security practices of your chosen wallet and multisig setup to ensure you’re using them correctly and securely.

Passphrase is not wallet password. Its a seed extension.
First create a new seed and backup the seed. You can use the same seed for all 4 wallets. Same seed, but 4 different passphrase. The passphrase can be a single word or any custom phrase.

On electrum proceed with I already have a seed, enter your seed. Now choose options and check “extend this seed with custom words”. Click Ok. On next screen you’ll be asked to enter your seed extension. Enter your custom phrase and proceed with the multisig setup.

The passphrase that you enter should be different for all 4 setups. When you want to restore the multisig setup you need the 24 word mnemonic seed as well as all the 4 custom passphrase.

Hi,
The question is, whether I could sign a transaction on the offline PC where I actually don’t have any balance? I didn’t try that yet.
I do therefore first sign the transaction on the online PC, where I received the BTC, then I export the transaction to an USB stick and then I sign the loaded transaction on the offline PC.
Then back again to the online PC and I broadcast the transaction.
Now I managed to build a 2of3 multisig wallet on the raspi.
I need to try it also, to use one seed for 4 multisig wallets.
With passphrase you mean the wallet password?
Of course I need to document everything for later, so I know exactly what I did.
Thanks a lot again…

Yes, 2 of 2 multisig wallet requires two signatures. Sign transaction on your offline PC, then copy the signed transaction to your online PC manually. Sign it there and broadcast the transaction.
For 2 of 4 multisig wallet only two signatures required. To send a transaction you can sign it from any two wallet. But to restore the complete 2 of 4 multisig wallet setup you need the seed and MPK of all 4 wallets.

Since you are doing it for your own family you can use same seed word with 4 different passphrase to setup 4 separate wallets or you can use 4 different mnemonic seed for all 4 wallets. Make sure to backup the seed words, passphrase and MPKs. You’ll need all this to restore the same 2 of 4 setup.

Before you transfer large amounts test it by sending a fraction of Bitcoin. Next delete the wallet and try restoring the same setup. If its successful then backup everything and write down all the process in your own style for future reference. Just in case if you forget how all of it works. You can now safely continue using your multisig wallet.

And under “outgoing payments” is the transaction with status = “Paid”.
Is the transaction in this case signed automatically?
Is the online wallet not considered a real multisig wallet?

The “wallet information” looks correct:
wallet type: 2of4
script type: p2sh
And any of the 4 MPKs are listed too…

I had expected to have to transfer the transaction to the offline wallet and sign it there too and then back to the online PC and send it to the recipient address.

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With your tutorial on the other hand it was a successful story!
This is (for me) the only tutorial which led me to a successfully building a multisig 2of2 wallet.
Only the point with spending BTC hasn’t been covered enough in my opinion.
How is it in general? Need I to be asked to sign the transactions or are they signed under the hood, automatically?
And I must copy the once signed Transaction before I copy it to the offline PC for the second signature (which I do manually)?
Any transaction needs two signatures in order to be ready to be sent out, correct?
OK, this was my first question.

The second one is:
How do I build a 2of4 multisig wallet on an (only one) offline pc?
I need it in order to securely leave the Bitcoins to my children.
Especially when the point comes to enter the MPKs of the cosigners (four in total).
Which MPK comes into which wallet and how to do that?
In case of just two wallets it’s actually quite easy. Just cancel the first wallet until I have the MPK of the second one,
which is being completed with the two MPKs.
But what is with the third and fourth wallet? Does every wallet need then the three MPKs from the other wallets,
so any wallet the own MPK and the ones of the other three cosigners?
Thanks