Is it necessary for every legal entity processing SEPA payment transactions in my organisation's group structure to adhere to the Scheme, even if its SEPA Scheme payments are “routed” through another legal entity in the group?

It is mandatory that all legal entities making and receiving SEPA Scheme payments will join the Scheme. It is possible for an entity in the same group to process payments in the way described, but in such a case the signing entity is fully responsible for all the obligations set out in the relevant Rulebook on behalf of the other group entity.