It's called a Bitcoin Fork. I wrote a topic about it years ago, although the values are much lower by now, and most Forkcoins are worthless. But you'll own a few dollars worth of Forkcoins too. Chances are it's going to a be lot of work to recover them from your multisig, so if you don't move them, just keep your multisig in case it becomes worth more in 10 years (which I don't expect to be very likely).

I've checked OP's address, and the equivalent BCash address contains around $5 worth of BCash. I've not bothered to check any other forks.

Langostas - I will PM you with my ProtonMail address, which you can use to send me your keys and password if you are happy to accept the risk of doing so. You can also send some of the information via ProtonMail and some of the information via forum PM to keep it separate, if you prefer. I'll take a look at them when I get chance over the weekend and confirm your receiving address before I send you your coins.