They have multisig but not ring sig.
nostr:nevent1qqswtkn39eey8fhc6ngfh04efezf3ueq2vq80xa0kxr6rgt8j6nrdkqpzamhxue69uhhyetvv9ujucm4wfex2mn59en8j6gpramhxue69uhkummnw3ez6un9d3shjtnzd96xxmmfdchxu6twdfssz9rhwden5te0wfjkccte9ehx7um5wghxyecpzfmhxue69uhk7enxvd5xz6tw9ec82csp89uq3
a federation can join this ring signature scheme?
Yes, I understand that.