So can I run on a multisig wallet too? I need it and two ln wallets that I created for the test. it turns out that all three should be run with this argument, right? All transactions with bitcoins there simply will not be present in the history later when to return to the main working network?
No, LN is only available for [standard] Native SegWit Electrum wallets.
Read the thread I linked above to learn more about the usage of Electrum's LN feature:
Electrum Lightning Network walkthroughTestnet funds have no value and in a separate blockchain than Bitcoin's.
You can easily get funds using testnet faucets:
List of Testnet BTC FaucetI mean that now I transfer over the real network first from a multisig wallet to two already existing LN. In the test network, how do I do that?