This document specifies the steps a host takes in deciding how to
autoconfigure its interfaces in IP version 6 (IPv6).
The autoconfiguration process specified in this document applies only
to hosts and not routers. Since host autoconfiguration uses
information advertised by routers, routers will need to be configured
by some other means.
IP - Internet Protocol Version 6. The terms IPv4 and IPv6 are used
only in contexts where necessary to avoid ambiguity.
node - a device that implements IP.
router - a node that forwards IP packets not explicitly addressed to
host - any node that is not a router.
The RFC makes it very clear that nodes that act as routers are NOT to use SLAAC for IPv6 address configuration. In other words, routers that derived their interface IPv6 address from SLAAC cannot act as routers on that link. The RFC pretty explicitly says so.
You CAN use DHCPv6, but DHCPv6 is NOT SLAAC. Sadly ROS doesn't implement DHCPv6 yet. Once it does there is theoretically nothing in the way of receiving a prefix via DHCPv6, assigning an address in that prefix on an interface, and sending RAs on that interface.
Specific answers require specific questions. When in doubt, post the output of "/ip address print detail", "/ip route print detail", "/interface print detail", "/ip firewall export", and an accurate network diagram.